wired up the inverter after adding second battery, switched on mains charger to get batteries fully charged before trying inverter, had a check round with voltmeter and got different readings from each battery, check all battery connections scratched head a bit and eventually found had forgoten to put a fuse in the fuse holder for the positive link between the batteries, my excuse is that I was trying to see best way of siting every thing so was trying different wiring directions from the fuse holder either straight through or 90 degree turn