AGM Batteries ‘Depth of Discharge’?

Since purchasing and installing four new ‘AGM’ batteries for our domestic bank I have been puzzling as to what their level of charge, or discharge is. They came with a 5 year warranty, but I suspect that is conditional on how they are maintained, or abused!

Firstly at what point are they requiring to be re-charged, or in other words ‘How Low Can You Go’…?

The supplier states that:

AGM Leisure batteries can be drained using 80% of their capacity. They can also be re-charged almost 3 times as fast as a conventional standard wet flooded leisure battery.”

But what is 80% capacity, and how is it measured?

The state of charge is measured by the voltage of the battery bank, and this chart shows battery condition vs voltage reading.

We are recommended to:

Remain in the ‘Green’ zone to maximise the batteries life although occasionally dropping down to 11.66V is permissible.” 

Secondly what is the maximum rate of charging they will accept…?

Fast re-charging is very useful, but at what rate? I am advised to set the charge controller as follows:

  • Max charge current 30A
  • Max voltage 14.30V
  • (set charge controller to AGM or GEL batteries)

That’s all there is too it… so I am told.

Since their installation our battery overnight voltage, has been held above 12.10V; despite demands from lighting, TV, water pumping, and fridge freezer.

Long may it continue.