How to Recharge an Absorbed Glass Mat

Absorbed glass mat (AGM) batteries are a relatively new type of highly efficient batteries that are capable of storing charges longer than traditional wet cell models. They contain plates that are placed closely to electrolyte solution, allowing faster charge and discharge rates than other lead acid type batteries. They tend to be more expensive alternatives, which is all the more reason to charge and discharge them according to their specifications. As long as you follow the correct steps, these batteries should last for hundreds of cycles.

AGM Battery
Multimeter
Battery charger/controller

Instructions

- 1
  Check the state of charge of your battery by connecting the positive and negative probes of a multimeter to the terminals on the battery with the dial set to measure DC voltage. Each cell in the battery should produce about 2.14 volts when fully charged, and 2.03 volts when at 50 percent. If needing to charge a 12-volt car battery, there will be 6 plates, meaning a voltage of greater than 12.8 would be full, while less than 12.1 would be less than 50 percent.
- 2
  Connect the battery to the charger/controller. For these batteries it would be wise to invest in an automatic charge controller to avoid overcharging the battery and damaging it for future use; these should be able to supply a bulk, absorption and float charge to the battery.
- 3
  Remove the battery from the charger when a sustained voltage of 2.14 volts or more per plate is measured. Measure the battery while it is disconnected from the charger for 10 to 20 seconds.
- 4
  Keep batteries connected to the charger, set on a trickle or float charge of about 13.2 to 13.6 volts while not in use. This will help to maintain the battery over periods of non-use, as otherwise charge will decrease over time, and dip below the 50 percent mark, potentially damaging the capacity of the battery.

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