What is an AGM Battery?

Absorbed glass mat batteries, or AGM batteries, became popular in the 1980s. They were used to power motorcycles, military, aircraft, and submarines, but now you can find them in everyday cars and trucks.

AGM batteries are a maintenance-free alternative to traditional flooded lead-acid batteries. They are designed to provide powerful bursts of starting amps and run electronics longer. 

How do AGM batteries work?

An AGM (absorbed glass mat) battery contains a special glass mat separator that wicks the electrolyte solution between the battery plates. This material’s design enables the fiberglass to be saturated with electrolytes – and to store the electrolyte in a “dry” or suspended state rather than in free liquid form.

As the battery works, the electrolyte is transferred from the glass mat to the battery plates as required. The mat contains enough electrolyte for the battery to deliver its total capacity, and – should the battery case become damaged, or the battery is tipped on its side – its electrolyte will not spill.

Pros and cons of AGM batteries?

Pros

These batteries are called maintenance-free batteries and do not require watering service. Since there is no free liquid and minimal gassing, AGM batteries can perform better than flooded batteries in applications where maintenance is complex.

Maintenance free

Long service life

High current delivery

Extremely low-maintenance: Does not require watering service, which lowers operating costs

Can perform better than flooded batteries in applications where maintenance is complex to perform

Can be installed sideways -- electrolyte will remain inside

Cons

Users should take care when charging this battery as over, and under-charging can affect their life and performance. AGM batteries perform most reliably when limited to discharge no more than 50% of battery capacity.

Take care when charging; over- and under-charging can affect life and performance

Limit discharge to 50% of battery capacity for the best reliability

Often higher up-front cost than lead-acid batteries (often 3X+ cheaper than lithium-ion, though)