Electrical problem

BillDavies

We have a Bessacarr E435 with a new leisure battery but the step no longer operates nor the internal lights. If I hook up to mains and put the battery selector to leisure battery everthing works. When not hooked up and leisure battery selected the needle
on the gauge creeps up but as soon as a light is switched on it drops to zero. Has anyone any ideas on wher I should look to sort this problem?