Lead Acid Deep Cycle Battery Voltage Chart

Lead-acid deep-cycle batteries are a widely used battery type for renewable energy storage, electric vehicles and backup power. They are widely used because of their ability to maintain good performance during frequent charging and discharging. Voltage is one of the key indicators of battery performance. Understanding the voltage characteristics of lead-acid deep-cycle batteries and their effects will not only help to manage the battery effectively, but also prolong its life.

How Lead Acid Deep Cycle Batteries Work

A lead-acid deep cycle battery, as the name suggests, is a lead-acid battery with a high depth of discharge. Its depth of discharge (DOD) is usually higher than 80%, which means it is able to release most of its charge. These batteries are designed to withstand frequent deep discharge and recharge cycles, hence the name ‘deep cycle battery’.

The principle of operation of a lead-acid deep cycle battery is based on the chemical reaction of lead and lead oxide in a sulphuric acid electrolyte. During discharge, lead (Pb) at the negative electrode reacts with sulphate ions (SO₄²-) in the electrolyte to form lead sulphate (PbSO₄) and release electrons. The lead oxide (PbO₂) at the positive electrode, in turn, reacts with hydrogen ions (H⁺) and electrons in the electrolyte to also form lead sulphate, and possibly release oxygen (although in sealed batteries, the oxygen is usually re-condensed back into the electrolyte). The charging process, then, is the reverse of these reactions, whereby current is supplied via an external power source to reconvert the lead sulphate back into lead and lead oxides, while restoring the electrolyte concentration.

Lead Acid Deep Cycle Battery Product Features:

• High Depth of Discharge: Lead-acid deep cycle batteries are capable of withstanding depths of discharge of up to 80% or more, which makes them excellent in applications that require frequent deep discharges.
• Long cycle life: Because they are designed for deep discharge, lead acid deep cycle batteries typically have a long cycle life of hundreds or even thousands of charge/discharge cycles.
• Cost Effective: The low cost of lead acid deep cycle batteries compared to other types of batteries makes them competitive in many applications.
• Simple Maintenance: Maintenance of lead acid deep cycle batteries is relatively simple and usually only requires regular checking of the electrolyte level and battery voltage.

Voltage Characteristics of Lead Acid Deep Cycle Battery

The voltage characteristics of lead-acid deep cycle batteries are one of their important properties, and the following is a detailed explanation of their voltage characteristics:

Open Circuit Voltage

The open-circuit voltage (i.e. the voltage without load) of a fully charged lead-acid deep cycle battery is usually around 13.1V. This voltage value is related to the sulphuric acid concentration of the battery, and some manufacturers use a high sulphuric acid concentration, so the open circuit voltage may exceed 13.5 V. The open circuit voltage is an indication of the state of charge of the battery, and the open circuit voltage will gradually decrease as the battery is discharged.

Float Charge Voltage

Float voltage is a voltage state maintained by a lead-acid deep cycle battery during the charging process. In the float state, the battery is connected to the charger, but the charger delivers less current, which is only used to compensate for the battery's self-discharge losses. The float voltage is usually set between 13.5 and 13.9V, a range that can be adjusted according to the specific type of battery and the manufacturer's recommendations. The float voltage is set to maintain the battery's state of charge while avoiding overcharging.

Deep Cycle Charging Voltage

The deep cycle charging voltage is the voltage at which the battery is charged at constant voltage while cycling the battery. Compared with the float charging voltage, the deep cycle charging voltage is higher, usually between 14.1 and 14.5V. This higher voltage is to increase the charging rate and ensure that the battery can be fully charged in a short period of time. During deep cycle charging, the battery is disconnected from the load to ensure charging efficiency and battery safety.

Voltage changes during discharge

During the discharge process, the voltage of the lead-acid deep cycle battery will change. At the beginning discharge stage, the battery voltage will rapidly drop from the open circuit voltage to a lower voltage level (e.g. 12.6V), which is mainly due to the consumption of sulfuric acid in the pole plate void. As the discharge proceeds, the amount of sulfuric acid replenishment and consumption gradually reaches a balance, and the battery voltage enters a relatively stable stage, when the voltage drops more steadily from a higher value to a lower value (e.g., from 12.6V to 11.1V). After a long period of stable discharge, the battery voltage will drop rapidly, indicating that the discharge is close to the end.

Lead Acid Deep Cycle Battery Voltage Charts

Below are 3 lead battery voltage charts for the most common lead acid battery voltages - 12V, 24V and 48V. Again, as a reminder, it's best to use the charts for lead batteries out of the box, but if you're just looking for a general guide, you can check out our charts below.

12V Lead Acid Battery Voltage Chart

While 12V lead acid batteries are widely used in rechargeable solar electric systems, portable solar generator pages often use 12V AGM sealed lead acid batteries with a front LCD display that shows the battery level so you know when it needs to be recharged.

According to the chart above, a 12V sealed lead-acid battery has a voltage of 12.89 volts in a fully charged state and 12.23 volts in a fully discharged state (assuming a maximum depth of discharge of 50%). This indicates a voltage difference of 0.66 volts between its charging from 100 per cent to 0 per cent.

In comparison, the 12V valve regulated lead acid battery has a fully charged voltage of 12.64 volts and a fully discharged voltage of 12.07 volts (again assuming a maximum depth of discharge of 50%). This gives a voltage difference of 0.57 volts from 100% to 0% charge.

24V Lead Acid Battery Voltage Chart

A 24V lead acid battery is another commonly used battery option for solar power systems particularly, those that provide bigger power capacity.

A 24V sealed lead acid battery is in its fully charged state at 25.77 volts and it is in a fully discharged state at 24.45 volts (assuming 50% max DOD). This is a full 1.32 volts difference between 100% and 0% charge.

With a full 1.15 volts difference between 100% and 0% charge. A 24V flooded lead acid battery, on the other hand, is in fully charged state at 25.29 volts and it is in a fully discharged state at 24.14 volts (assuming 50% max DOD).

48V Lead Acid Battery Voltage Chart

48V lead-acid batteries are commonly used by telecoms companies for backup power. In addition, they are also used in high power capacity solar generators

According to the above chart, a 48V sealed lead-acid battery has a voltage of 52.00 volts in the fully charged state and 48.20 volts in the fully discharged state (assuming a maximum depth of discharge of 50%). Therefore, the voltage difference between charging from 100% to 0% is 3.80 volts.

In comparison, a 48V valve-regulated lead-acid battery has a fully charged voltage of 50.92 volts and a fully discharged voltage of 48.40 volts (again assuming a maximum depth of discharge of 50%). This indicates a voltage difference of 2.52 volts between 100 per cent and 0 per cent discharge.

Effect of Lead Acid Deep Cycle Battery Voltage on Battery Performance

Lead-acid deep-cycle batteries are an important source of energy widely used for power storage and electric vehicles, but their battery performance is greatly affected by their voltage state. Understanding the effect of voltage on battery performance can help optimise the use and maintenance of batteries and extend their life. Below are a few important aspects of lead-acid deep cycle battery voltage that affect its performance:

1. Charging efficiency

The charging efficiency of lead-acid deep cycle batteries is directly related to the battery voltage. The correct charging voltage can ensure that the battery is fully charged in time, while too high or too low charging voltage may lead to inadequate charging process. Too low a charging voltage may cause the battery not to be fully charged and not be able to reach the ideal storage state, resulting in a reduction of capacity; while too high a charging voltage may cause gassing and overcharging, or even lead to internal damage and shorten the life of the battery.

2. Discharge performance

During the discharge process, the change of battery voltage can reflect the health status and remaining capacity of the battery. When lead-acid deep cycle battery is discharged, its voltage decreases gradually. Under normal circumstances, the voltage at the end of discharge should be kept within the safe range (usually 10.5V to 11.8V). If discharged to too low a voltage (e.g. below 10.5V), it will cause the battery to be affected by sulphation, which will reduce the effective capacity of the battery and shorten its service life.

3. Cycle life

The cycle life of a battery is closely related to its voltage management. Lead-acid deep-cycle batteries operating under prolonged high voltage (overcharge) and low voltage (overdischarge) conditions will accelerate internal corrosion and aging, reducing the cycle life of the battery. A reasonable voltage range ensures that the battery maintains good chemistry during charging and discharging, which in turn extends the battery's life.

4. Temperature effects

Voltage and temperature are closely related, especially in the charging and discharging process of lead-acid batteries. Higher voltage brings more heat, and high temperature may lead to evaporation of water from the battery, exacerbating the increase of electrolyte concentration, which not only affects the performance of the battery, but also may lead to battery failure. Monitoring and regulating the temperature to keep it in the appropriate range can effectively maintain the voltage status and performance of the battery.

5. Battery Balancing

In a multi-cell system, the voltage balance between cells is very important. Voltage differences between different battery packs may cause some cells to discharge or charge prematurely, thus affecting overall performance. Regular equalisation charging ensures that all batteries are maintained at similar voltage levels, improving overall system performance and stability.

How to Measure Lead Acid Deep Cycle Battery Voltage

Measuring the voltage of a lead-acid deep cycle battery is usually done using a digital multimeter or a battery tester. Firstly, set the measuring instrument to the appropriate voltage range, then touch the probes to the positive and negative terminals of the battery respectively and read the displayed voltage value. Before taking the measurement, make sure the battery is not loaded to get a more accurate reading. Regular voltage checks are an important part of maintaining the performance of lead-acid batteries.

Maintaining and Managing Lead Acid Deep Cycle Batteries

Lead-acid deep-cycle batteries are used in a variety of applications such as electric vehicles, solar energy storage systems and uninterruptible power supplies (UPS) due to their stability and relatively low cost. To ensure that these batteries maintain optimal performance, regular maintenance and management is important. Below are some key maintenance and management recommendations:

1. Check voltage regularly

• Frequency: Measure the voltage of the battery using a digital multimeter on a regular basis, and it is recommended to check it at least once a month.
• Normal range: The normal static voltage of a lead-acid deep-cycle battery is usually between 12.4V and 13.2V. Ensuring that the battery is within this range can be effective in prolonging its life.

2. Maintaining Electrolyte Levels

• Check the level: Check the level of the battery regularly to ensure that the electrolyte (a mixture of sulphuric acid and water) is at the proper level. When the electrolyte is below the electrode surface, it may cause battery damage.
• Add distilled water: If necessary, use distilled water to replenish the electrolyte, but avoid adding too much. It is generally recommended to add it before charging to reduce water evaporation.

3. Prevent overcharging and overdischarging

• Charge management: Use a suitable charger to ensure that the charging process will not be overcharged, and the charger should be equipped with an automatic charging stop function.
• Discharge limitation: Avoid discharging batteries to very low voltages (usually below 10.5V) to prevent severe sulphation of the batteries and reduction of their capacity and service life.

4. Regular Cleaning

• Keep the exterior of the battery clean: Clean dirt and corrosion from the battery surface regularly to ensure good contact. Clean the battery terminals with a solution of baking soda mixed with water and rinse well with water.
• Check connections: Ensure the tightness of the connection terminals to prevent loose connections from arcing, accelerating corrosion, or causing battery performance degradation.

5. Temperature control

• Ambient Temperature: Avoid operating the battery at extremely high or low temperatures, the ideal operating temperature is 0°C to 25°C. Higher temperatures accelerate evaporation, while lower temperatures affect the rate of electrochemical reaction.
• Prevent heat build-up: Ensure that there is good ventilation around the battery to avoid overheating that could lead to performance degradation.

6. Regular Equalisation Charging

• Equalisation charging: For multi-battery systems, carry out equalisation charging on a regular basis to ensure that the voltage of each individual battery is the same and to improve the overall performance.
• Preventive measures: When equalising charging, pay attention to prevent overcharging of individual batteries to avoid damage.

7. Monitor and record usage

• Usage record: It is recommended to record the usage of the battery regularly, including charging and discharging cycles, running time and voltage changes, so as to facilitate the tracking of the battery status.
• Maintenance records: Keeping a maintenance log to record the contents of each inspection and maintenance will help to identify potential problems and respond to them in a timely manner.

FAQ

What is the normal voltage of a lead-acid deep cycle battery?

The normal voltage range of lead acid deep cycle batteries is usually between 12V and 13.8V (for 12V batteries). During charging, the voltage may rise to 14V to 14.8V, and during discharging, the voltage will gradually drop to about 10.5V, which should be considered for recharging.

How to judge whether a lead-acid deep cycle battery needs to be replaced?

If the battery's voltage does not return to the normal range after charging, or if the battery's capacity drops significantly (e.g., it can only discharge half or less of its original capacity), the battery may need to be replaced. In addition, if the battery is leaking, deformed or swollen, it should also be replaced immediately.

Can lead-acid deep-cycle batteries be fast-charged?

Although lead-acid deep cycle batteries can be rapid-charged, frequent rapid-charging will accelerate the aging process and shorten the battery life. Therefore, it is recommended that frequent rapid charging be avoided as much as possible and that slower charging rates be used to extend the life of the battery.

When discharging, can the lead-acid battery be completely emptied?

It is not recommended to completely discharge lead-acid batteries. Frequent deep discharging will shorten battery life.

Is it necessary to recharge lead-acid deep cycle batteries regularly?

Yes, lead-acid deep cycle batteries that are not used for a long period of time need to be recharged periodically to avoid lead sulphate crystallisation and to maintain battery activity.