Charging batteries while on hookup

churrilman

When on hook up neither batteries are charging,checked voltage of both batteries reading around 12.6 volts, switch engine on and readings are 14 volts, On hookup both batteries show no increase. Checked fuses near hab battery and engine battery all
ok.consumer unit in van has a red indicator which doesn't light but all the 240 van electrics are working. Any help would be much appreciated.Van is a self build(not me)professionally done.

I assumed that on hookup the batteries would be charged but on our first trip out 2 nights both the lesuire and engine batteries flattened and had to call the AA out.