These lead acid battery voltage charts for 6V, 12V, and 24V batteries, as well as 2V lead acid cells, indicate the state of charge dependent on voltage.
Based on factors like temperature, discharge rate, and battery type, lead acid battery voltage curves may vary significantly (e.g. sealed, flooded).
The general, averaged charts for voltage to battery capacity mentioned below should never take priority over them.
It should be noted that using open circuit voltage to gauge the level of charge of batteries is only reliable when the batteries are at room temperature and have had many hours to rest without any loads or chargers.
Table of Contents
Charts for 6V Lead Acid Batteries
Batteries, 6V Sealed Lead Acid (AGM & Gel)
| Voltage | Capacity |
|---|---|
| 6.44V | 100% |
| 6.39V | 90% |
| 6.33V | 80% |
| 6.26V | 70% |
| 6.20V | 60% |
| 6.11V | 50% |
| 6.05V | 40% |
| 5.98V | 30% |
| 5.90V | 20% |
| 5.85V | 10% |
| 5.81V | 0% |
Downloadable Chart
Lead acid batteries with a voltage of 6V
| Voltage | Capacity |
|---|---|
| 6.32V | 100% |
| 6.26V | 90% |
| 6.20V | 80% |
| 6.15V | 70% |
| 6.09V | 60% |
| 6.03V | 50% |
| 5.98V | 40% |
| 5.94V | 30% |
| 5.88V | 20% |
| 5.82V | 10% |
| 5.79V | 0% |
Downloadable Chart
Notes
Some DC equipment including lights, pumps, and electric motorcycles utilize 6V lead acid batteries.
A 12V battery bank may also be made by wiring two together in series.
Three 2V lead acid cells are connected in series to create them.
Assuming a maximum depth of discharge of 50%, 6V sealed lead acid batteries reach full charge at roughly 6.44 volts and reach full discharge at around 6.11 volts.
Assuming a maximum depth of discharge of 50%, 6V flooded lead acid batteries reach full charge at roughly 6.32 volts and reach full discharge at around 6.03 volts.
Related Also: How to Wire RV Batteries?
Charts for 12V Lead Acid Batteries
Sealed lead acid batteries, 12 volts (AGM & Gel)
| Voltage | Capacity |
|---|---|
| 12.89V | 100% |
| 12.78V | 90% |
| 12.65V | 80% |
| 12.51V | 70% |
| 12.41V | 60% |
| 12.23V | 50% |
| 12.11V | 40% |
| 11.96V | 30% |
| 11.81V | 20% |
| 11.70V | 10% |
| 11.63V | 0% |
Downloadable Chart
Flooded lead acid batteries 12 volts
| Voltage | Capacity |
|---|---|
| 12.64V | 100% |
| 12.53V | 90% |
| 12.41V | 80% |
| 12.29V | 70% |
| 12.18V | 60% |
| 12.07V | 50% |
| 11.97V | 40% |
| 11.87V | 30% |
| 11.76V | 20% |
| 11.63V | 10% |
| 11.59V | 0% |
Downloadable Chart
Notes
Solar power systems and other 12V electrical systems often use 12V lead acid batteries.
They come at a modest initial cost and are readily accessible.
12V lead acid batteries are often used in automobiles and boats.
They are created by stringing together six 2V lead acid cells.
Lead acid rechargeable batteries continue to be the most common kind for home solar power systems, as far as I can determine.
But lately, lithium iron phosphate (LiFePO4) batteries have gained a lot more traction, mostly as a result of the sharp price reductions we’ve witnessed over the last ten years.
Assuming a maximum depth of discharge of 50%, 12V sealed lead acid batteries reach full charge at around 12.89 volts and reach complete discharge at about 12.23 volts.
Assuming a maximum depth of discharge of 50%, 12V flooded lead acid batteries reach full charge at around 12.64 volts and reach complete discharge at about 12.07 volts.
Recommended reading: Why Does My RV No Power from Battery?
Charts for 24V Lead Acid Batteries
Sealed lead acid batteries for 24V (AGM & Gel)
| Voltage | Capacity |
|---|---|
| 25.77V | 100% |
| 25.56V | 90% |
| 25.31V | 80% |
| 25.02V | 70% |
| 24.81V | 60% |
| 24.45V | 50% |
| 24.21V | 40% |
| 23.91V | 30% |
| 23.61V | 20% |
| 23.40V | 10% |
| 23.25V | 0% |
Downloadable Chart
Batteries, 24V Flooded Lead Acid
| Voltage | Capacity |
|---|---|
| 25.29V | 100% |
| 25.05V | 90% |
| 24.81V | 80% |
| 24.58V | 70% |
| 24.36V | 60% |
| 24.14V | 50% |
| 23.94V | 40% |
| 23.74V | 30% |
| 23.51V | 20% |
| 23.27V | 10% |
| 23.18V | 0% |
Downloadable Chart
Notes
Another typical alternative for solar power systems is 24V lead acid batteries.
By reducing amperage while working with greater voltages, you may spend less on wiring and equipment.
They are created by connecting two 12V lead acid batteries or twelve 2V lead acid cells in series.
Assuming a maximum depth of discharge of 50%, 24V sealed lead acid batteries reach full charge at around 25.77 volts and reach complete discharge at about 24.45 volts.
Assuming a maximum depth of discharge of 50%, 24V flooded lead acid batteries reach full charge at around 25.29 volts and reach full discharge at about 24.14 volts.
Charts for 2V Lead Acid Cell Voltage
Lead Acid Cells, 2V Sealed (AGM & Gel)
| Voltage | Capacity |
|---|---|
| 2.15V | 100% |
| 2.13V | 90% |
| 2.11V | 80% |
| 2.09V | 70% |
| 2.07V | 60% |
| 2.04V | 50% |
| 2.02V | 40% |
| 1.99V | 30% |
| 1.97V | 20% |
| 1.95V | 10% |
| 1.94V | 0% |
Downloadable Chart
Lead acid batteries with a 2V flood
| Voltage | Capacity |
|---|---|
| 2.11V | 100% |
| 2.09V | 90% |
| 2.07V | 80% |
| 2.05V | 70% |
| 2.03V | 60% |
| 2.01V | 50% |
| 1.99V | 40% |
| 1.98V | 30% |
| 1.96V | 20% |
| 1.94V | 10% |
| 1.93V | 0% |
Downloadable Chart
Notes
The nominal voltage of a single lead acid battery is 2 volts (sometimes listed as 2.1 volts).
You may purchase 2V lead acid cells and link them in series-parallel arrangements to create a battery bank with the voltage and capacity you want.
Taking a 50% maximum depth of discharge as an example, 2V sealed lead acid batteries are completely charged at around 2.15 volts and fully discharged at roughly 2.04 volts.
A 50% maximum depth of discharge results in a full charge of 2.11 volts for 2V flooded lead acid batteries and a complete discharge of 2.01 volts.
Related Also: 10 Tips for RV Battery Maintenance
3 Ways to Check the Capacity of a Lead Acid Battery
#1. Using a multimeter, measure the open circuit voltage
Pros:
- Reliable
Cons:
- The battery needs to rest for many hours when all loads and charges are unplugged.
Disconnect everything from your battery and let it to sit at room temperature for several hours before attempting to estimate battery capacity based on open circuit voltage.
(Battery University advises a minimum of 4 hours.)
Simply measure the voltage at the battery terminals using a multimeter and then compare the result to the state of charge table in your battery handbook.
If there isn’t a chart in your battery handbook, use the relevant one from the list above.
For instance, I recently wanted to check the amount of power left in a sealed lead acid battery I possess that is 12V 33Ah.
The battery had been laying unconnected in my basement for the previous several weeks; it was already at rest and at room temperature.
In order to test DC voltage, I took my multimeter and set it up before touching the probes to the battery terminals.
12.63 volts were measured as the open circuit voltage.
I was unable to locate my battery’s handbook, so I made an estimate of its capacity using the 12V sealed lead acid voltage table above.
That graphic led me to believe that it still had roughly 80% of its capability.
#2. Using a hydrometer or refractometer, check specific gravity
Pros:
- Reliable
Cons:
- Only effective with flooded lead acid batteries
Your lead acid battery’s “specific gravity” may be determined with a hydrometer or refractometer.
Another method to determine the state of charge is to calculate the specific gravity.
This technique only works with flooded batteries since it necessitates opening the battery to reach the electrolyte solution within.
I’ve only ever worked with sealed lead acid batteries, so I’m afraid I can’t walk you through the process.
Consult your battery’s instruction manual, as well as the manuals for your hydrometer and refractometer, for further information.
#3. Implement a solar charge controller.
Pros:
- Convenient
Cons:
- Unreliable
Your charge controller most likely monitors battery voltage for you if you’re using a lead-acid battery in a solar power system.
You could believe that you can just use this information to determine your battery’s capacity.
Unfortunately, it is quite incorrect to estimate capacity using battery voltage when the battery is linked to chargers and loads.
Variables like temperature and discharge rate have a big impact on battery voltage.
Additionally, certain charge controllers may not accurately read the battery voltage.
Some charge controllers merely show the last decimal place, while others have large error margins.
One inexpensive PWM charge controller, for instance, that I tested said that the battery voltage margin of error was 0.2 volts.
However, I am certain that the majority of DIY solar enthusiasts will utilize this reading often, if not always.
To more correctly gauge your battery’s level of charge, you have to unhook everything and let it rest.
If that describes you, just be aware of how erratic this number may be.
Don’t assume you can use it to determine the exact charge level of your battery.
Use it just to gain a broad notion of how much charge or discharge your battery has, if at all.
FAQ about Lead Acid Voltage
Reminder: The recommended voltages and state of charge chart in the handbook that came with your battery should be followed instead of the general ones provided here.
What voltage does a 12V lead acid battery have when it is completely charged?
When completely charged, an unloaded 12V sealed lead acid battery will have an open circuit voltage of around 12.9 volts.
When completely charged, a 12V flooded lead acid battery will have an open circuit voltage of around 12.6 volts.
You must first unplug the battery from all loads and chargers and allow it to sit at room temperature for many hours before you can determine a battery’s capacity from its voltage.
What is the lead acid battery’s 12V minimum operating voltage?
A 12V sealed lead acid battery’s lowest open circuit voltage is around 12.2 volts, assuming a maximum depth of drain of 50%.
A 12V flooded lead acid battery’s minimum open circuit voltage, assuming a 50% maximum depth of drain, is around 12.1 volts.
How far can a lead acid battery be discharged?
Most lead acid batteries can only be partially discharged.
More discharge might harm them permanently.
Lead acid batteries should never be discharged to 100% depth of discharge.
This may significantly reduce its longevity.
Here is a graph demonstrating the association between lead acid battery life cycles and depth of discharge for non-deep-cycle batteries:
You can see that a lead acid battery’s lifetime may be significantly shortened by regularly discharging it to 100%.
What is a 12V lead acid battery’s float voltage?
A sealed 12V lead acid battery typically has a float voltage of 13.6 volts plus or minus 0.2 volts.
A flooded 12V lead acid battery typically has a float voltage of 13.5 volts.
Follow the suggested float voltage described in your battery’s handbook as always.
Sometimes, the float voltage will even be indicated on your battery label.
Some manufactures refer to float as “standby.”
How I Obtained the Data for These Charts
I checked up the datasheets for 7 well-known lead acid battery manufacturers to get the figures in the voltage charts above.
In order to get the final figures, I located the state of charge charts in each and averaged them all.
The datasheets I utilized (2 AGM, 2 gel) for the sealed lead acid values are shown below, along with the page number where I discovered the voltage chart:
– Power-Sonic (pg. 10)
– Fullriver (pg. 23)
– Universal Battery (pg. 2)
– Renogy (pg. 4)
The ones I used for the flooding values are listed below:
– Crown (pg. 6)
– Trojan Battery (pg. 1)
– OutBack Power (pg. 8)
These charts weren’t made with precise precision.
Only a few of the datasheets provided accurate open circuit voltages by capacity in a tabular format.
They often included a graph that I had to extrapolate the values from.
The graphs also often included broad bands rather than narrow lines, as if to represent a margin of error or a range of potential values.
I eventually came to understand that this was a way for the brands to avoid presenting an exact figure.
Only for capacity values of 0%, 25%, 50%, 75%, and 100% did other brands supply precise statistics.
I had to develop linear functions from them to estimate the values that lay between them.
To generate the figures for 6V, 12V, and 24V batteries, I first computed all the numbers for 2V lead acid cells, then multiplied those numbers by the appropriate number of cells in series.
The values were all rounded to two decimal places at the end.
Reference:
- https://footprinthero.com/lead-acid-battery-voltage-charts
