Browse technical resources about commercial solar, energy storage, EMS/BMS/PCS, microgrids, and peak arbitrage.
HOME / Evaluating Battery Charger Voltage - VLM Commercial ESS
These solar-integrated backup power units combine photovoltaic generation, lithium battery storage, and smart energy control into a compact, transportable container—delivering reliable electricity whenever and wherever it's needed.
The nominal voltage of lead acid is 2 volts per cell, however when measuring the open circuit voltage, the OCV of a charged and rested battery should be 2.
The 24V lead-acid battery state of charge voltage ranges from 25.46V (100% capacity) to 22.72V (0% capacity). 48V Lead-Acid Battery Voltage Chart (4th Chart). The 48V lead-acid battery state of charge voltage ranges from 50.92 (100% capacity) to 45.44V (0% capacity). Lead acid battery is comprised of lead oxide (PbO2) cathode and lead (Pb) anode.
Here we see that a 6V lead acid battery has an actual voltage of 6V at a charge between 40% and 50% (43%, to be exact). The voltage spans from 6.37V at 100% charge to 5.71V at 0% charge. It is also important to note that lead batteries have a depth of discharge (DoD) close to about 50%.
A lead acid battery is considered fully charged when its voltage level reaches 12.7V for a 12V battery. However, this voltage level may vary depending on the battery's manufacturer, type, and temperature. What are the voltage indicators for different charge levels in a lead acid battery?
12V lead acid batteries are popular in solar power systems and other 12V electrical systems. They're widely available and have a low upfront cost. Many car and marine batteries are 12V lead acid batteries. They are made by connecting six 2V lead acid cells in series.
The 48V lead-acid battery state of charge voltage ranges from 50.92 (100% capacity) to 45.44V (0% capacity). Lead acid battery is comprised of lead oxide (PbO2) cathode and lead (Pb) anode. The medium of exchange is sulphuric acid. Most common example of lead-acid batteries are car batteries.
For lead-acid batteries, including VRLA (Valve-Regulated Lead-Acid) and AGM (Absorbent Glass Mat) types, typical values range from 12.6 to 12.8 volts when fully charged. The state of charge (SOC) refers to the battery's remaining energy level. It is often measured using open circuit voltage, which is the voltage of a battery at rest.
Root cause 1: High self-discharge, which causes low voltage. Solution: Charge the bare lithium battery directly using the charger with over-voltage protection, but do not use universal charge.
Part 3. Why is it bad to fully discharge a lithium-ion battery? Fully discharging a lithium-ion battery can harm it for a variety of reasons: Voltage drops below safe levels: Lithium-ion batteries have a safe operating voltage range, typically between 3.0V and 4.2V per cell.
Fully discharging a lithium-ion battery can harm it for a variety of reasons: Voltage drops below safe levels: Lithium-ion batteries have a safe operating voltage range, typically between 3.0V and 4.2V per cell. Dropping below 3.0V can cause internal damage, leading to capacity loss or even rendering the battery unusable.
The memory effect occurs when a battery “remembers” a smaller capacity due to repeated partial discharges. Since lithium-ion batteries don't experience this issue, there's no need to fully discharge them before recharging. Part 6. Can a fully discharged lithium-ion battery be revived?
The voltage of a lithium-ion battery system always fluctuates during charging or discharging. If you see the voltage during charge or discharge cycles, you will notice that the voltage remains constant initially and then varies over time. In the discharge cycle, initially, the voltage will be 4.2V.
Overcharging and over-discharging lithium-ion batteries can compromise their safety, sometimes leading to fires or other serious accidents. The voltage limits of a battery are a key consideration when designing charging circuits to ensure safe operation.
Root cause 1: High self-discharge, which causes low voltage. Solution: Charge the bare lithium battery directly using the charger with over-voltage protection, but do not use universal charge. It could be quite dangerous. Root cause 2: Uneven current.
Lithium-Iron Phosphate (LiFePO4) is a natural mineral that was identified for use as a cathode in 1996 and since then has gained considerable acceptance in the market. Due to low electrical conductivity, many developments have been made to help increase its performance such as coating the particles in carbon. Lithium is the lightest of all metals and has the highest electrochemical potential, which offers a much better power-to-weight ratio when compared with traditional wet-lead acid batteries and means that you can get. Having a Battery Management System (BMS) is extremely important with Lithium batteries. These systems will disconnect the charging/discharging. Lithium batteries are temperature sensitive so care needs to be taken so they are not charged at low temperatures. Charging lithium batteries at. Lithium batteries require a different charging profile to wet lead-acid batteries. A mains charger with only a lead-acid charge profile would partially recharge a lithium battery, however, it is extremely unlikely it would reach.
[PDF Version]It is also recommended that you check out the lithium-ion battery voltage chart to understand the voltage and charge of these batteries. The recommended voltage range for short-term storage of lithium-ion batteries is 3.0 to 4.2 volts per cell in series.
The most important key parameter you should know in lithium-ion batteries is the nominal voltage. The standard operating voltage of the lithium-ion battery system is called the nominal voltage. For lithium-ion batteries, the nominal voltage is approximately 3.7-volt per cell which is the average voltage during the discharge cycle.
Different lithium battery materials typically have different battery voltages caused by the differences in electron transfer and chemical reaction processes. Most popular voltage sizes of lithium batteries include 12V, 24V, and 48V.
The lithium-ion battery voltage chart is an important tool that helps you understand the potential difference between the two poles of the battery. The key parameters you need to keep in mind, include rated voltage, working voltage, open circuit voltage, and termination voltage.
The key parameters you need to keep in mind, include rated voltage, working voltage, open circuit voltage, and termination voltage. Different lithium battery materials typically have different battery voltages caused by the differences in electron transfer and chemical reaction processes.
Lithium batteries are becoming more popular in the leisure market and many people are looking to upgrade to this more efficient technology. Unfortunately, simply upgrading the battery may not be enough and fundamental changes may need to be made to your 12V set-up.
Lithium-ion battery voltage chart represents the state of charge (SoC) based on different voltages. This Jackery guide gives a detailed overview of lithium-ion batteries, their working principle, and which Li-ion power. Lithium-ion batteries are rechargeable battery types used in a variety of appliances. As the name defines, these batteries use lithium-ions. Lithium-ion batteries are known for having a high energy density due to the highly reactive lithium inside them. Some features of lithium-ion batteries include: 1. High-Energy Density:. Thanks to their safe nature, lithium-ion batteries are common in solar generators. Different voltages sizes of lithium-ion batteries are available, such as 12V, 24V, and 48V. The lithium-ion. Jackery manufactures high-quality power stations and solar generators to help people switch to clean and green energy. Jackery Explorer Power Stations are portable batteries made with lithium-ion or LiFePO4. Most Jackery.
[PDF Version]Lithium-ion batteries are most used in power stations and solar systems, all thanks to the built-in additional layer of security. The popular voltage sizes of lithium-ion batteries include 12V, 24V, and 48V. Let's understand the discharge rate of a 1-cell lithium battery at different voltages. Lithium-ion Battery Voltage Chart:
The lithium-ion battery voltage chart is an important tool that helps you understand the potential difference between the two poles of the battery. The key parameters you need to keep in mind, include rated voltage, working voltage, open circuit voltage, and termination voltage.
The key parameters you need to keep in mind, include rated voltage, working voltage, open circuit voltage, and termination voltage. Different lithium battery materials typically have different battery voltages caused by the differences in electron transfer and chemical reaction processes.
The ideal voltage for a lithium-ion battery depends on its state of charge and specific chemistry. For a typical lithium-ion cell, the ideal voltage when fully charged is about 4.2V. During use, the ideal operating voltage is usually between 3.6V and 3.7V. What voltage is 50% for a lithium battery?
The SoC voltage chart for lithium batteries shows the voltage values with respect to SoC percentage. A Li-ion cell when fully charged at 100%SoC can have nearly 4.2V. As it starts to discharge itself, the voltage decreases, and the voltage remains to be 3.7V when the battery is at half charge, ie, 50%SoC.
The most important key parameter you should know in lithium-ion batteries is the nominal voltage. The standard operating voltage of the lithium-ion battery system is called the nominal voltage. For lithium-ion batteries, the nominal voltage is approximately 3.7-volt per cell which is the average voltage during the discharge cycle.
Apply a saturated charge to prevent sulfation taking place. With this type of battery, you can keep the battery on charge as long as you have the correct float voltage. For larger batteries, a full charge can take up to 14 or 16 hours and your batteries should not be charged using fast charging methods if. Sealed lead-acid batteries can ensure high peak currents but you should avoid full discharges all the way to zero. The best recommendation is to. As with all batteries, take care of and handle your batteries appropriately and if you are unsure or have further questions, consult the manual provided. To prolong the lifespan of a sealed. Although perfectly safe when used correctly, sealed lead-acid batteries are rated as toxic and need to be disposed of correctly. This type of battery is not one that you can dispose of. If you need to put your battery into storage, keep it above 2.05V and apply a topping charge every six months to keep the battery in tip-top.
[PDF Version]The most important first step in charging a lead-acid battery is selecting the correct charger. Lead-acid batteries come in different types, including flooded (wet), absorbed glass mat (AGM), and gel batteries. Each type has specific charging requirements regarding voltage and current levels.
Proper monitoring during charging is crucial for safety and performance. Lead-acid batteries produce hydrogen and oxygen gases as they charge, particularly in the later stages of charging. These gases can accumulate and become hazardous if not properly ventilated.
As with all other batteries, make sure that they stay cool and don't overheat during charging. Sealed lead-acid batteries can ensure high peak currents but you should avoid full discharges all the way to zero. The best recommendation is to charge after every use to ensure that a full discharge doesn't happen accidently.
current limited charging is best.To charge a sealed lead acid battery, a DC voltage between 2.30 volts per cell (float) and 2.45 volts per cell (fast) is applie to the terminals of the battery. Depending on the state of charge (SoC), the cell may temporarily be lower after d scharge than the applied voltage. After some t
The lead acid chemistry is fairly tolerant of overcharging, which allows marketing organizations to get to extremely cheap chargers, even sealed lead acid batteries can recycle the gasses produced to prevent damage to the battery as long as the charge rate is slow.
Even in storage, lead-acid batteries naturally lose charge over time, and failure to periodically recharge them can result in irreversible damage. 8. Proper Disposal and Recycling of Lead-Acid Batteries Lead-acid batteries contain hazardous materials, including lead and sulfuric acid, making proper disposal crucial.
Standard Voltage: Most solar panels, especially smaller ones, operate around a nominal voltage of 12V. Using the formula with our 25-watt panel, Amps=25W12V Amps=2.
A 25-watt solar panel can generate approximately 25 watt-hours of energy under optimal conditions every sunny hour. It might seem limited for household appliances. However, a 25-watt solar panel can power various smaller devices and applications.
For a 25 watt solar panel, you'd need a 12v 30Ah lead-acid or 12v 20Ah lithium-ion battery. To calculate the size of a battery, multiply the highest number of peak sun hours your location receives (by month, In my case its 6.9 in April) by the solar panel rated wattage and then divide the value by 12 for 12v battery
At daytime the 25W solar panel charges a 12V battery inside the control unit, which then provides power to 4 x 5W 12V LED lights connected via front sockets on the control unit. In addition, there's a standard 5V USB socket for charging mobile phones and USB compatible devices.
Under optimal conditions, a 25-watt solar panel can produce just a little over 2 amps of current at 12 volts.
But if you have a 25w solar panel most probably you'll use it to charge your cellphone, laptop, or maybe a few other small appliances. so i recommend a jackery explorer 240 portable solar generator which will make your life easier.
But you wanna run a small appliance so you'll need an inverter or if you're using multiple 25w solar panels your total output will be higher. so a 50w pure sine wave inverter is recommended for 25w solar panels, keep in mind that the inverter will cause a 15% of loss in current when converting DC into AC.
Currently, there are three main categories of charging methods for lithium-ion batteries: CC-CV charging, pulse current charging, and multi-stage constant current charging.
There are two main methods of charging a battery: Constant current method. In this charging method the batteries are charged at a constant current. The charging current is set by introducing some resistance in the Circuit. This method has its own drawbacks because the state of charge Of the battery is not taken into account.
When charging a lithium-ion battery, the charger uses a specific charging algorithm for lithium-ion batteries to maximise their performance. Select LI-ION using the MODE button.
A method of continuously charging the battery with a small current. Its name derives from the trickle of water. Although the charging time is longer, the advantage is that the battery is not affected even if a small current continues to flow in a fully charged state.
In the initial stage of charging, the battery is charged using a constant power charging method until the battery voltage reaches the upper limit voltage (4.2 V).
The MCC method is suitable for charging the following battery types: lead-acid, NiMH, and Li-ion batteries. With equal initial current values, the MCC charging process takes a bit more time compared to the CC-CV charging method.
During the initial phase of charging, the method utilizes constant loss charging until the battery terminal voltage reaches the upper limit voltage (4.2 V). The loss is defined as the square of the current multiplied by the battery's equivalent impedance, which varies with the battery's remaining capacity.
The Equalizer is a small device that actively equalizes the voltage between battery packs. When it detects a voltage difference between different battery Cells, it kicks in and actively transfers energy from the battery with the higher voltage to the battery with the slightly lower voltage. This creates a voltage balance. There are a few reasons that batteries may start to experience voltage imbalances. Some of the most common causes of voltage imbalance in batteries include: over charging, over discharging, sulfation (the build-up of. There are two aspects to consider, one is the type of battery, different types require different equalisers, and the other is the size of the battery pack, which must be fitted with equalisers of the same size or used in parallel. Let us talk. Usually in a battery bank, there will be several batteries connected in parallel or in series. as there is no same battery, it may cause charge and. Lead acid batteries are a popular type of battery that use lead and lead acid materials to create an electric current. Lead acid batteries come in many shapes, sizes and capacities, but.
[PDF Version]Battery equalization voltage refers specifically to the specific voltage that must be applied to many batteries in order not to overcharge or undercharge them, while equalizing charge ensures batteries of all types receive an even amount of charge.
Voltage equalization means that the voltages across all cells in a battery pack are at the same level or within a specific range of each other. When cells within a battery pack have different voltage levels, it can negatively impact the overall performance and longevity of the battery pack.
The concept of using battery pack capacity as the equalization objective is that all cells are theoretically fully charged or discharged at the same time. Thereby it can avoid reaching cell cut-off voltages and make the battery stop charging or discharging even when the capacity or SOC is not zero, thus maximizing capacity utilization.
The Equalizer is a small device that actively equalizes the voltage between battery packs. When it detects a voltage difference between different battery Cells, it kicks in and actively transfers energy from the battery with the higher voltage to the battery with the slightly lower voltage.
By equalizing the cells, the battery pack can operate at its optimal level, maximizing its capacity and extending its lifespan. Equalization also helps to prevent premature cell failure and minimizes the risk of damage caused by overcharging or over-discharging.
The process of equalization typically involves applying a higher voltage or current to the battery, allowing the cells to reach their maximum charge capacity. This helps to equalize the voltage levels and capacity of each cell, bringing them back into balance.
Our portable electronic devices like smartphones, smartwatches, laptops, torches, and power banks, etc all these things require some portable supply of energy to use these devices. The conventional AC sup. Different parameters of the battery define the characteristics of the battery, which include terminal voltage, charge storage capacity, rate of charge-discharge, battery cost, charge-disc. Many parameters are required for the selection of the battery for a particular application, such as voltage rating, current rating, life cycle, charge capacity rating and so on which differ. It is desired that batteries used in the solar PV system should have low self-discharge, high storage capacity, rechargeable, deep discharge capacity, and convenience for service. For suc. This part can be categorized into two parts first is replacing the battery bank with a new one and the second is a complete installation and commissioning of the battery bank. To.
[PDF Version]Usually, batteries with 6 V and 12 V are available for the solar PV system application. Now each battery is made up of cells and depending on the material its terminal voltage of the cell is determined.
Different parameters of the battery define the characteristics of the battery, which include terminal voltage, charge storage capacity, rate of charge-discharge, battery cost, charge-discharge cycles, etc. so the choice to select batteries for a particular solar PV system application is determined by its various characteristics.
Appropriate battery terminal voltage must be chosen for the application or it might not work, sometimes it requires 3 V, sometimes 6 V, or sometimes even 12 V or higher. Usually, batteries with 6 V and 12 V are available for the solar PV system application.
The charge storage capacity of the battery is reflected by its physical size. Small size batteries have small storage of charge while large size batteries have high storage of charge. One of the most commonly used batteries in the solar PV system is the lead-acid battery.
In the standalone PV application, we require higher voltage or higher current or sometimes both to meet our load requirement. The number of batteries required to meet our load demand depends on the level of voltage and current we require at the battery array terminal.
The battery monitoring will measure and displayed on the LCD (Liquid Crystal Display) the several parameters of the PV system such as voltage, current, solar irradiance, ambient and cell temperature of the Stand-alone PV system.
The best storage voltage for lithium-ion batteries should be stored at whatever voltage is required to be at around 60-70% of its maximum charge voltage when not in use.
Best working temperatures are between 15°C and 35°C. Proper lithium-ion batteries storage is critical for maintaining an optimum battery performance and reducing the risk of fire and/or explosion. Many recent accidents regarding lithium-ion battery fires have been connected to inadequate storage area or conditions.
The best storage voltage for lithium titanate oxide (LTO) cells is between 2.4V and 2.5V per cell, and for lead acid batteries, it's around 2 volts per cell or 12 volts for a typical battery. Ideally, you should have a designated area that you use solely for lithium-ion battery storage.
Requirements for Lithium –Ion batteries placed on the European Union market in accordance with the Batteries Directive 2006/66/EC, Regulation 1103/2010 and Directive 2023/56/EU, and corresponding national laws. Batteries may be classified as hazardous waste in some EU countries. The batteries have to be marked with the crossed wheel bin symbol.
The ideal surface for storing lithium-ion batteries is concrete, metal, or ceramic or any non-flammable material. Batteries can be stored in a metal cabinet such as a chemical-storage cabinet, make sure that batteries are not touching each other. It is recommended to have in place a fire detector in the storage area.
Lithium-ion battery fires can even reignite after being contained. In this post, we'll talk through the safe storage requirements for lithium-ion batteries that manage the risks to keep people and facilities safe. The UK doesn't have specific regulations or legislation for the general storage of lithium-ion batteries.
The UK doesn't have specific regulations or legislation for the general storage of lithium-ion batteries. The Health and Safety Executive has, however, published guidance on good practices for handling and storing batteries, even though it is not compulsory. Regulations are not prescriptive but instead follow the typical routes:
Charging Current and Battery Capacity: A general guideline is to select a charger that provides a charging current of about 10% of the battery's amp-hour (Ah) rating.
10.4.1.2 Output Voltage. Since the recharge voltage required varies with the ambient temperature and the particular type of battery used, the charger should be selected for the particular type of batteries being used and the anticipated ambient temperature range. It is recommended that the output voltage be adjustable. Size.
The charging current for the battery is 10A±10% or 7.5A±10% or 5A±10% or 4A±10% or 3A±10% or 2A±0.3A or 1.5A±0.3A. The Maxxlee BCS0227 Smart Battery Charger is compatible with 12V & 24V lead-acid batteries (WET, MF, AGM and GEL).
– It is recommended that the charging current be equal to one tenth of the capacity (e.g. 44Ah divided by 10 = 4.4A charging current). – The temperature of the acid may not exceed 55°C during charging. If the temperature rises above 55°C, the charging process must be discontinued.
The charge algorithm of the charger must fit the battery type connected to the charger. The following table shows the three predefined battery types available. A custom battery type can be programmed by the user. Charging voltages at room temperature: For 24V battery chargers: multiply all values by 2.
When charging a lithium-ion battery, the charger uses a specific charging algorithm for lithium-ion batteries to maximise their performance. Select LI-ION using the MODE button.
A custom battery type can be programmed by the user. Charging voltages at room temperature: For 24V battery chargers: multiply all values by 2. NORMAL (14.4V): recommended for wet-cell flat-plate lead-antimony batteries (starter batteries), flat-plate gel and AGM batteries.
These are the most critical settings that need to be done carefully for the better functioning of the solar charge controller. A solar charge controller is capable of handling a variety of battery voltages ranging from 12 v. While you set up your new solar charge controller, you should begin with properly wiring the controller to the battery bank and solar panels properly. Once the wiring is properly done an. After the solar charge controller settings for a 12V system, the 24V system is the most common charge controller used in residential solar power systems. The basic settings for this a. Before you begin setting up your lithium batteries, remember that lithium batteries do not require temperature compensation. Also, if you are replacing lead batteries with lithium batteries. The lead acid battery is a classic configuration in a solar power system. Once you convert the battery type from lithium/AGM to lead acid battery, the original set para.
[PDF Version]A solar charge controller is capable of handling a variety of battery voltages ranging from 12 volts to 72 volts. As per the basic solar charge controller settings, it is capable of accommodating a maximum input voltage of 12 volts or 24 volts. You need to set the voltage and current parameters before you start using the charge controller.
When it comes to solar charge controller voltage settings there are several voltages involved: Charging Voltages Charge: The Bulk charge Stage consists of approximately 80% of the charge volume, where the charger current remains constant (in a constant current charger) and the voltage increases.
Set the absorption charge voltage, low voltage cutoff value, and float charge voltage according to your battery's user manual. Adjusting these settings helps prevent battery damage and promotes efficient charging. Start Charging: Your solar charge controller is ready to go once all these settings are adjusted!
In addition to lead-acid and lithium, Morningstar solar charge controllers can also charge nickel, aqueous hybrid ion, and flow or redox flow batteries. Solar charge controllers put batteries through 4 charging stages: Bulk, Absorption, Float, and Equalization. Read more today.
Solar charge controllers put batteries through 4 charging stages: What are the 4 Solar Battery Charging Stages? For lead-acid batteries, the initial bulk charging stage delivers the maximum allowable current into the solar battery to bring it up to a state of charge of approximately 80 to 90%.
Solar charge controllers have different settings that need to be adjusted in order for them to work properly. They set up the output parameters of the power so that the battery bank can be charged at the most optimal voltage.
The cost to replace a hybrid battery usually ranges from $2,000 to $8,000. Key factors include the battery type, warranty, and whether a dealer or aftermarket provider handles the installation.
Scroll down to get the lowdown on hybrid battery replacement costs in the UK. How much does a hybrid battery replacement cost? On average, replacing a hybrid battery will cost upwards of £2,000 in the UK. Of course, the cost will depend on the make and model of the car, its age and, therefore, its parts availability.
One of the primary factors that can affect the cost of replacing a hybrid car battery is the make and model of the vehicle. Different manufacturers use different types of battery technology, which can significantly impact the price. Additionally, the size and capacity of the battery can also influence the cost.
Being smaller than a standard EV battery, a hybrid battery is cheaper to replace, but it can still be quite expensive. A big factor in price is how old and what make the hybrid car is. Unlike replacing a regular 12-volt car battery, the batteries in hybrid and electric vehicles require specialised tooling and know-how.
Additionally, the age of the car can affect the cost of replacing the battery. As hybrid cars age, their batteries may degrade and lose capacity. In some cases, older batteries may need to be replaced entirely. However, newer hybrid cars may still be under warranty, which can significantly reduce the cost of replacement.
In the UK, there are warranties and guarantees offered for hybrid car battery replacement, providing peace of mind to owners. Most hybrid car manufacturers offer a warranty on the battery for a certain period of time or mileage.
It may be time to consider replacing the battery in your vehicle if it is getting close to reaching this milestone. It is possible for the cost of replacing a hybrid battery to change based on the brand and model of your car, as well as the location where the repair is performed.
However, to make batteries last, there is no need to remove them, just make sure to unplug the bass between practices. That should extend battery lifetime.
Of course, you could have gotten a battery that was in the bass longer, or played a lot at the store before you took it home, IDK, anything is possible with the battery that come with the bass, but if you put one in, it should not bother you for a while.
Yes, you must unplug the bass, that is the cord from the bass itself, not just the amp. When you insert the jack, that is the “ON” switch for your active bass, it will drain battery up until you remove the cord, or it drains. I have a bass I play every day, it has the battery that came with the bass, and its been about 3 months and it is fine.
If a bass has an active/passive switch it is guaranteed to have passive pickups (active/passive switches do not work with active pickups). With an active/passive switch, it may or may not prevent battery drain while the bass is plugged in. It depends on the bass. Hmm. I did not know that about bass pick ups.
That should extend battery lifetime. Yes, you must unplug the bass, that is the cord from the bass itself, not just the amp. When you insert the jack, that is the “ON” switch for your active bass, it will drain battery up until you remove the cord, or it drains.
By definition, a Battery Energy Storage Systems (BESS) is a type of energy storage solution, a collection of large batteries within a container, that can store and discharge electrical energy upon request.
The cable still being plugged in was your big problem for sure, but always remember that not all batteries even of the same type/brand won't last the same. Depending on how long they have been sitting on the shelf, storage temp and factors like that, you might get 4 months from one and 6 from the next.