Anyone have a ton of experience with these things, as the stages increase so the calls for replacement batteires increases.

What I am looking for is a 12 VDC 100amp/hr drop in battery which can be connecte din series to make 24 VDC and charger using the inverter charger.

The amount of money required to upgrade the batteries to lithium, it might pay to fit a proper lithium change and a relay, when the power is on the relay is open and the charger charges the battery, when the power drops, the relay closes and the battery feeds the inverter, simple.

We are in for over R10 000 for drop in batteries, whats anotehr R3k for a lithium charger? still going to be cheaper than buying a lithium mobile unit.