The article discusses lead-acid batteries, focusing on sealed types commonly used in solar setups. These batteries are sealed and require minimal maintenance compared to flooded types. Two main types are AGM and Gel batteries. AGM batteries have fiberglass mats that absorb electrolytes, while Gel batteries use a gel-like substance.
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Both types are durable and require little maintenance. The article includes charts showing voltage levels for different states of charge for 12V, 24V, and 48V AGM and Gel batteries, ranging from 100% charge to 0%. The charts help users understand the relationship between voltage and battery capacity, crucial for managing solar power systems.
Lead Acid batteries are affordable and reliable ways to store energy being produced by your solar system. A lead acid deep cycle voltage chart tells you the relationship between the state of charge and the voltage the battery can produce.
Lead acid batteries can be split up into two groups: sealed and flooded types.
We're going to be focusing on the former and looking at various lead acid deep cycle battery voltage charts to get a better understanding of the data.
Sealed Lead Acid Battery Voltage Chart
The Sealed Lead Acid battery used falls under the valve-regulated lead acid battery group.
These lead acid batteries are more common in the world of solar compared to their flooded counterparts. A quality deep-cycle solar battery system can run you a good few hundred dollars, but they're well worth the investment.
Sealed lead acid batteries are rechargeable and the main distinction between them and flooded is that they are sealed with an electrolyte that isn't free-flowing.
This brings with it several advantages.
The hydrogen gas generated during charging cycles in a sealed battery is reabsorbed into the electrolyte. A safety vent stops the gases from building up too much pressure.
As a result, the sealed battery requires fewer periodic top-ups of distilled water and has less electrolyte loss.
Due to excessive charging resulting in gassing and water depletion, sealed lead acid batteries are made with a minimal over-voltage potential to prevent the battery from reaching its gas-generating potential during charge.
So when we look at a sealed AGM 12V battery voltage chart and compare it to a wet cell battery of the same capacity, the results favor the sealed battery,
As a result, these batteries are never able to be fully charged. Lead calcium is used in sealed lead-acid batteries rather than lead antimony to lessen dry-out.
Types of Sealed Lead-Acid Batteries
There are 2 types of sealed lead-acid batteries: AGM batteries and Gel-based batteries.
Whenever you see an AGM battery's resting voltage chart and you feel like you don't know what these batteries are or what affects their values, you should read up on the battery itself.
AGM batteries perform better than wet cell batteries in practically every category. Concerning total weight and charge cycles, these lead acid batteries are the best.
The electrolytes can be absorbed by the AGM lead acid batteries, which are mounted between two fiberglass mats.
A unique glass mat separator found in an AGM battery secures the electrolyte solution between the battery plates.
Due to this, electrolytes can be stored in a dry or suspended condition rather than as a free liquid since the fiberglass can be saturated with it.
Electrolytes are moved from the glass mat to the battery plates as needed during the operation of the battery.
The battery's electrolyte won't spill if the battery case is destroyed or it is turned on its side since the mat has enough electrolytes to allow the battery to operate at full capacity.
A gel battery is a valve-regulated, lead-acid battery that combines silica fumes with an electrolyte in a predetermined amount of sulfuric acid.
The immobile, gel-like substance produced by this chemical reaction is what gives these batteries their name.
The one-way valves allow the internal gasses to recombine into the water, therefore eliminating the need to top off distilled water or check the water level.
As a result, the gel batteries require almost little maintenance. Gel batteries are incredibly durable and adaptable.
They have extremely low gas output, so they are safe to be installed in locations with restricted ventilation, thus you can even install the batteries inside your home.
We will look at both sealed-type batteries when displaying the battery volt charts and see how they compare to each other.
Battery Charging Lead Acid Battery Voltage Chart
Voltage measurement of charge is straightforward but prone to error due to temperature and cell material effects on voltage.
Batteries must initially rest in an open circuit state for at least four hours to obtain an accurate reading using the voltage method, while most battery manufacturers advise waiting for 24 hours.
As a result, measuring batteries that are actively and continuously in use is not appropriate using the voltage approach.
A hydrometer is used to measure the relative density of liquids based on buoyancy to calculate specific gravity, which is then used to calculate the charge.
The weight of the battery's active chemicals is monitored by the hydrometer as it discharges.
The specific gravity of a battery reduces proportionally when the amount of sulfuric acid in the active electrolyte decreases as a result of use.
Battery SoC Chart
State of Charge (SoC) refers to the capacity that is now accessible. The state of charge value ranges from 0% to 100%.
A battery is fully charged if the state of charge is 100%, whereas a rating of 0% means the cell is completely discharged.
As the value cannot rise above 50% in real-world applications, the cell is recharged once the state of charge hits that level.
Similar to this, the maximal state of charge starts to drop as the battery ages, meaning a 100% state of charge for an old battery would be similar to a 75%'80% state of charge for a young one.
We're going to have a look at both types of sealed lead acid batteries and see whether they are the same or vastly different.
12V Lead Acid Battery Voltage Chart
The chart below shows the state of charge voltage of a 12V AGM battery. It ranges from 13.00V at 100% capacity to 10.50V at 0% capacity.
If you measure the 12.30V voltage on your 12V AGM battery, for example, you can determine that this 12V AGM battery still has 70% capacity.
Voltage
Capacity
13.00V
100% (charging)
12.85V
100% (resting)
12.80V
99%
12.75V
90%
12.50V
80%
12.30V
70%
12.15V
60%
12.05V
50%
11.95V
40%
11.81V
30%
11.66V
20%
11.51V
10%
10.50V
0%
The chart below shows the data for a 12V gel sealed lead acid battery, The values range from 11.80V at 0% to over 12.85 once it reaches 100% state of charge.
Voltage
Capacity
12.85V +
100%
12.65V
75%
12.35V
50%
12.00V
25%
11.80
0%
24V Lead Acid Battery Voltage Chart
When looking at a 24V battery voltage chart for an AGM sealed lead acid battery, it has a voltage range of 26.00V at 100% charge to 21.00V at 0% charge.
A full battery has a voltage differential of 5.00V from an empty battery.
This figure shows that a 24V battery has 20% to 30% charge left if the voltage difference between the cathode and anode of an AGM battery is measured to be 23.50V using a voltage meter.
Voltage
Capacity
26.00V
100% (charging)
25.85V
100% (resting)
25.75V
99%
25.55V
90%
25.00V
80%
24.60V
70%
24.30V
60%
24.10V
50%
23.90V
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40%
23.62V
30%
23.32V
20%
23.02V
10%
21.00V
0%
The data for a 24V gel sealed lead acid battery is displayed in the chart below. Values range from 23.80V at zero charges to over 24.85 at full charge.
Voltage
Capacity
24.85V +
100%
24.65V
75%
24.35V
50%
24.00V
25%
23.80V
0%
48V Lead-Acid Battery Voltage Chart
The 48V battery voltage chart for a gel-sealed lead-acid battery found below varies from 52.00V at 100% charge to 42.00V at 0% charge.
A full battery has a 10.00V absolute voltage difference from an empty battery.
This chart indicates that this 48V battery still has 20% to 30% charge left if the voltage difference between the cathode and anode of an AGM battery is measured to be 47.00V using a voltage meter.
Voltage
Capacity
52.00V
100% (charging)
51.70V
100% (resting)
51.45V
99%
51.10V
90%
50.00V
80%
49.20V
70%
48.60V
60%
48.20V
50%
47.80V
40%
47.24V
30%
46.64V
20%
46.04V
10%
42.00V
0%
The data for a 48V gel sealed lead acid battery is displayed in the chart below. Values range from 47.80V at zero charge to over 48.85 at full charge.
Voltage
Capacity
48.85V +
100%
48.65V
75%
48.35V
50%
48.00V
25%
47.80V
0%
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Dependable performance and long service life of your sealed lead acid battery will depend upon correct battery charging. Following incorrect charging procedures or using inadequate charging equipment can result in decreased battery life and/or poor battery performance. The selection of a suitable SLA battery charger and the methods used to charge it is just as important as choosing the right battery for the application.
Power Sonic recommends you select a charger designed for the chemistry of your battery. This means we recommend using a sealed lead acid battery charger, like the the A-C series of SLA chargers from Power Sonic, when charging a sealed lead acid battery.
Sealed lead acid batteries may be charged by using any of the following charging techniques:
To obtain maximum battery service life and capacity, along with acceptable recharge time and economy, constant voltage-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 applied to the terminals of the battery. Depending on the state of charge (SoC), the cell may temporarily be lower after discharge than the applied voltage. After some time, however, it should level off.
During charge, the lead sulfate of the positive plate becomes lead dioxide. As the battery reaches full charge, the positive plate begins generating dioxide causing a sudden rise in voltage due to decreasing internal resistance. A constant voltage charge, therefore, allows detection of this voltage increase and thus control of the current charge amount.
During constant voltage or taper charging, the battery's current acceptance decreases as voltage and state of charge increase. The battery is fully charged once the current stabilizes at a low level for a few hours. There are two criteria for determining when a battery is fully charged: (1) the final current level and (2) the peak charging voltage while this current flows.
Typical sealed lead acid battery charge characteristics for cycle service where charging is non-continuous and peak voltage can be higher.Typical characteristics for standby service type battery charge. Here, charging is continuous and the peak charge voltage must be lower.Selecting the appropriate charging method for your sealed lead acid battery depends on the intended use (cyclic or float service), economic considerations, recharge time, anticipated frequency and depth of discharge (DoD), and expected service life. The goal of any charging method is to control the charge current at the end of the charge.
Constant voltage charging is the best method to charge sealed lead acid batteries. Depending on the application, batteries may be charged either on a continuous or non-continuous basis. In applications where standby power is required to operate, for example a security system or uninterruptible power supply (UPS), when the AC power has been interrupted, continuous float charging is recommended. Non-continuous cyclic charging is used primarily with portable equipment where charging on an intermittent basis is appropriate, such as electric wheelchairs and mobile medical carts.
The constant voltage charge method applies a constant voltage to the battery and limits the initial charge current. It is necessary to set the charge voltage according to specified charge and temperature characteristics. Inaccurate voltage settings can cause either over-charge or under-charge. This charging method can be used for both cyclic and standby applications.
Constant voltage charging circuitConstant voltage charging characteristicsConstant current charging is suited for applications where discharged ampere-hours of the preceding discharge cycle are known. Charge time and charge quantity can easily be calculated, however an expensive circuit is necessary to obtain a highly accurate constant current. Monitoring of charge voltage or limiting of charge time is necessary to avoid excessive overcharge of the battery.
While this charging method is very effective for recovering the capacity of a SLA battery that has been stored for an extended period of time, or for occasional overcharging to equalize cell capacities, it lacks specific properties required in today's electronic environment.
The taper current charging method is not recommended as it is somewhat abusive of sealed lead acid batteries and can shorten service life. However, because of the simplicity of the circuit and low cost, taper current charging is extensively used to charge multiple numbers and/or for cyclic charging.
When using a taper current battery charger the charger time should be limited or a charging cut-off circuit needs to be incorporated to prevent over-charge.
In a taper current charging circuit, the current decreases in proportion to the voltage rise. When designing a taper charger always consider power voltage fluctuations. In this event the internal resistance drop will convert to heat. Heat generated by the circuit should be measured and if required a heat sink should be incorporated in the design.
Taper current charging circuitTaper current charging characteristics for this type of basically unregulated chargerAs a result of too high a charge voltage excessive current will flow into the battery, after reaching full charge, causing decomposition of water in the electrolyte and premature aging.
At high rates of overcharge a battery will progressively heat up. As it gets hotter, it will accept more current, heating up even further. This is called thermal runaway and it can destroy a battery in as little as a few hours.
If too low a charge voltage is applied, the current flow will essentially stop before the battery is fully charged. This allows some of the lead sulfate to remain on the electrodes, which will eventually reduce battery capacity.
Batteries which are stored in a discharged state, or left on the shelf for too long, may initially appear to be 'open circuited' or will accept far less current than normal. This is caused by a phenomenon called 'sulfation'. When this occurs, leave the charger connected to the battery. Usually, the battery will start to accept increasing amounts of current until a normal current level is reached. If there is no response, even to charge voltages above recommended levels, the battery may have been in a discharged state for too long to recover, and in which case a replacement SLA battery will be needed.
Cyclic (or cycling) applications generally require recharging be done in a relatively short time. The initial charge current, however, must not exceed 0.30 x C amps. Just as battery voltage drops during discharge, it slowly rises during charge. Full charge is determined by voltage and inflowing current. When, at a charge voltage of 2.45 ± 0.05 volts/cell, the current accepted by the battery drops to less than 0.01 x C amps (1% of rated capacity), the battery is fully charged and the charger should be disconnected or switched to a float voltage of 2.25 to 2.30 volts/cell. The voltage should not be allowed to rise above 2.45 ± 0.05 volts/cell.
Standby applications generally do not require that the battery be charged as fast or as frequently as in cycle operation. However, the battery must be kept constantly charged to replace the energy that is expended due to internal loss and deterioration of the battery itself. Although these losses are very low in Power Sonic lead acid batteries, they must be replaced at the rate the battery self discharges; at the same time the battery must not be given more than these losses or it will be overcharged. To accomplish this, a constant voltage method of charging called standby or float charging is used.
The recommended constant float voltage is 2.25 ' 2.30 volts per cell. Maintaining this float voltage will allow the battery to define its own current level and remain fully charged without having to disconnect the charger from the battery. The trickle current for a fully charged battery floating at the recommended charge voltage will typically hover around the 0.001C rate (7mA for a 7AH battery, for example.)
The float charger is basically a constant voltage power supply. As with cycle chargers, care must be taken not to exceed the initial charge current of 0.30 x C amperes.
This method uses two constant voltage devices. In the initial charge phase the high voltage setting is used. When charging is nearly complete and the charge voltage has risen to a specified value (with the charge current decreased), the charger switches the voltage to the lower setting. This method allows rapid charging in cycle or float service without the possibility of overcharging, even after extended charging periods.
Dual stage current limited SLA battery chargerTwo-step constant voltage charging characteristics.Lead acid batteries are strings of 2 volt cells connected in series, commonly 2, 3, 4 or 6 cells per battery. Strings of lead acid batteries, up to 48 volts and higher, may be charged in series safely and efficiently. However, as the number of batteries in series increases, so does the possibility of slight differences in capacity. These differences can result from age, storage history, temperature variations or abuse.
Fully charged batteries should never be mixed with discharged batteries when charging batteries in series. The discharged batteries should be charged before connection.
When a single constant voltage charger is connected across an entire high voltage string, the same current flows through all cells in the string. Depending on the characteristics of the individual batteries, some may overcharge while others remain in a slightly undercharged condition.
To minimize the effects of individual battery differences, use batteries of the same age, manufacturer, amp hour, and history and, if possible, charge in strings of no greater than 24 or 48 volts.
Lead acid batteries may be used in parallel with one or more batteries of equal voltage. When connecting batteries in parallel, the current from a charger will tend to divide almost equally between the batteries. No special matching of batteries is required. If the batteries of unequal capacity are connected in parallel, the current will tend to divide between the batteries in the ratio of capacities (actually, internal resistances).
When charging batteries in parallel, where different ratios of charge are to be expected, it is best to make provisions to assure that the currents will not vary too much between batteries.
Power Sonic sealed lead acid batteries perform well both at low and high temperatures. At low temperatures, however, charge efficiency is reduced; at temperatures above 45°C (113°F), charge efficiency increases so rapidly that there is a danger of thermal runaway if temperature compensation is not precise.
The effect of temperature on charge voltage is less critical in float applications than in cyclic use, where relatively high charge currents are applied for the purpose of short recharge times.
Temperature effects should definitely be considered when designing or selecting a charging system. Temperature compensation is desirable in the charging circuit, especially when operating outside the range of 5°C to 35°C
(41°F to 95°F). The temperature coefficient is -2mV/cell/ºC below 20°C (68°F) in float use and -6mV/cell/ ºC below 20°C in cyclic use. For higher temperatures the charge voltage should be correspondingly decreased.
The battery temperature compensation chart below shows the recommended charge voltages for different temperatures based on ambient charge voltage per cell.
TemperatureCyclic Use (V)Float Use (V)-40°C (-40°F)2.85 ' 2.952.38 ' 2.43-20°C (-4°F)2.67 ' 2.772.34 ' 2.39-10°C (14°F)2.61 ' 2.712.32 ' 2.370°C (32°F)2.55 ' 2.652.30 ' 2.°C (50°F)2.49 ' 2.592.28 ' 2.°C (68°F)2.43 ' 2.532.26 ' 2.°C (77°F)2.40 ' 2.502.25 ' 2.°C (86°F)2.37 ' 2.472.24 ' 2.°C (104°F)2.31 ' 2.412.22 ' 2.°C (122°F)2.25 ' 2.352.20 ' 2.25All batteries lose capacity through self-discharge, it is recommended that a 'top up charge' be applied to any battery that has been stored for a long period of time, prior to putting the battery into service.
To successfully top up charge a battery stored for more than 12 months, the open circuit voltage must be higher than 2.0 volts per cell, in this case, always confirm open circuit voltage prior to attempting top up charging.
The charging efficiency (η) of a battery is expressed by the following formula:
The charging efficiency varies depending upon the state of charge of the battery, temperatures, and charging rates. The below graph illustrates the concept of the state of charge and charging efficiency.
The below graph shows Power Sonic sealed lead acid batteries exhibit very high charging efficiency, even when charged at low charging rates.
It is always important to match your charger to deliver the correct current and voltage for the battery you are charging. For example, you wouldn't use a 24V charger to charge a 12V battery.
If you have any questions about an existing charger's capability with one of our products, please give us a call or send us an . We would be happy to assist you with your charging needs.
Contact us to discuss your requirements of 12 volt deep cycle agm battery. Our experienced sales team can help you identify the options that best suit your needs.