The lead acid battery can be divided into the flooded cell and the sealed lead acid battery. And the sealed lead acid category can be further split into AGM and gel cell batteries.

Each deep cycle battery type has its advantages and disadvantages, and you’ll have to decide what works best for you.

Let’s now look at these battery types separately:

1. Flooded Lead Acid
The standard flooded lead acid battery is the oldest car battery type in use.

In the flooded battery, lead plates are submerged in an electrolyte mix of sulfuric acid and water. The chemical reaction during charging and discharging produces gases that are vented from the battery.This creates a drop in the electrolyte level, which needs to be periodically topped up.The usable capacity of a flooded lead acid battery falls around 30-50%.

Usable capacity indicates how much of a battery can be used before it must be recharged — in this case, it’s up to 50% of the total capacity.

Charging a flooded battery happens in stages, which leaves room for undercharging or overcharging. On average, the charging efficiency of the flooded battery is around 70-85%.While the flooded battery is affordable, reliable, and tolerant of overcharging, it requires proper ventilation, must always be upright (to avoid electrolyte leakage), and needs the most maintenance. It also has a shorter lifespan compared to other types.

2. Absorbent Glass Mat (AGM)
The AGM battery is a type of Valve Regulated Lead Acid (VRLA) battery.

AGM is short for Absorbent Glass Mat, which refers to the thin fiberglass mats placed between the lead plates. The glass mat absorbs electrolyte, keeps it from moving and spilling, and acts as a damper between the lead plates.

The damping action of the glass mat makes the battery shock and vibration resistant, with the ability to withstand cold temperatures.

The AGM deep cycle battery has low internal resistance and charges faster than a flooded battery or gel battery. It has a 95% charge efficiency and an 80% Depth of Discharge (DoD).

The AGM battery’s many advantages include being maintenance-free, position insensitive, durable and fast-charging. However, it’s more expensive than the flooded cell battery and is sensitive to overcharging, so it needs a regulated charger.

3. Gel Cell
The gel cell battery is another one of the VRLA batteries (like the AGM battery).

The gel battery uses a gelled electrolyte, formed from (typically) sulfuric acid and water suspended in a silica agent.

The gel battery has a charge efficiency of around 85-90%, with excellent heat tolerance and no off-gassing.

However, this battery can’t tolerate fast charging. The gelled electrolyte is also very sensitive to overcharging and can be irreparably damaged if this happens.

The gel cell battery is maintenance-free, spill-proof, position insensitive with a high tolerance to heat. But it’s also more costly than flooded or AGM batteries and needs a special charger and regulator.