How To Charge An AGM Battery And Its Types

The best alternative of conventional acid batteries are automotive AGM batteries. The AGM battery is quite different in its characteristics including how to charge them. If you are going to buy an AGM battery, first read these charging instructions that will help you understand the mechanism of the battery. It also helps to extend the battery life.

Instructions On How To Properly Charge An AGM Battery

Car owners often think that charging batteries is a time-consuming task that is best left to the experts. However, the battery for the car is easy to charge. You just need to choose the right charger and follow a number of recommendations from experts.

There are two types of devices for charging car batteries:

  • Automatic;

In mechanical type devices, the one who uses them has to independently regulate the voltage and current strength. Automated devices must be selected immediately with 2 modes of operation – recharging and storage.

In addition, when choosing a charger, the following criteria should be considered:

  1. Charging current display function
    Modern charging devices are equipped with LCD monitors that display all the necessary information.
  2. Battery type
    It is important to consider the type of energy source before selecting a device for battery charging. For example, stations for recharging liquid acid batteries are not suitable for charging helium or AGM models.
  3. Temperature compensation
    While charging, the battery temperature can increase significantly. This process can also be enhanced by high temperatures at the place where the charge is made.
    If the charger is not equipped with a temperature compensation function, this may cause the battery to be overcharged, which will adversely affect its life. It is better to select models of chargers with built-in temperature sensors.
  4. Charging stages
    It is important to consider this characteristic when you are using charger to service lead-acid batteries.
  5. Adjustable fan speed
    This characteristic determines the efficiency of cooling and the life of the device for recharging. The function of controlling the speed of rotation of the cooling valves makes it possible to reduce the noise during the operation of the device or reduce its temperature, preventing overheating of the entire equipment.
  6. Operating temperature range
    Classic models of chargers can operate at temperatures ranging from +5…+45°C. In addition, devices with a wider temperature range are on sale. This technique is designed specifically for professional use. If the battery will be recharged in an unheated room or in the fresh air, this characteristic must also be taken into account when selecting.

Standard Procedure

The classic charging of an AGM type car battery consists of several stages:

  • First, the dead battery is removed from the car. In this case, safety requirements must be taken into account.
  • The place where the battery will be charged must be protected from negative external factors (chemicals, combustible mixtures, flames, etc.).
  • The battery is connected to the device for recharging, which is connected to the mains.
  • The charger automatically adjusts to the voltage and current of the battery.
  • Then it remains only to wait until the battery is fully charged. After the procedure is completed, the charged and ready-to-use device is installed back into the car.

Three-stage Charging

Experts note that the method of three-stage battery recharging is the most effective. However, manufacturers of such devices rarely mention it. This is due to a number of difficulties associated with three-stage charging.

The procedure is as follows:

  1. First, the AGM battery is charged at 10-30% of its capacity at a voltage of 14.2 to 14.8 V. This cycle is the main one and makes it possible to compensate for about 80% of the entire capacity.
  2. After that, a cumulative cycle is performed. At this stage, the minimum current strength of 0.3 V is set on the device for recharging. The battery charge reaches 100% in 3-3.5 hours.
  3. The third stage is floating charging. In this mode, the voltage of the device varies from 13.2 to 13.8 V.

Two Stage

The principle of this technique is similar to the three-stage recharging. However, in the two-stage method, there is no floating charge mode.


The principle of recharge is that a floating current with a voltage of 13.2 to 13.8 V is supplied to the battery. Battery manufacturers do not recommend using recharge to restore completely dead devices. In such situations, multi-stage charging is better suited.

Note: This mode is used only for quick charging of the device. It is not used as the main method.

Basic Recommendations For The Charging Process

Before recharging an AGM battery, you should familiarize yourself with the stages of this process:

  • Main – battery capacity is restored by 80%;
  • Floating – the capacity of the energy source is restored to a value of 100%;
  • Storage – at this stage, the AGM type battery consumes a minimum of current from the recharging device;
  • Storage – the battery normalizes and fixes its operational parameters.

AGM batteries need to be charged using a specialized device that can determine the voltage and current strength. These characteristics must be controlled, otherwise an undesirable process of gas formation may occur inside the battery.

Note: Do not charge AGM batteries with standard chargers. For this purpose, it is better to use special stations with smart control. Such devices will allow you to charge the AGM in a gentle mode.

During the charging procedure, it is necessary to control the temperature indicators of the electrolyte. They should not be higher than +50°C, otherwise the battery life will be reduced.

In addition, if a voltage of more than 15.2 V is used for recharging, then hydrolysis will begin to occur in the device, which will lead to the loss of water from the electrolyte and the formation of a gas cushion. This will negatively affect the condition of the AGM battery.

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