I had a leisure battery 85 ah, but have been charging it with a charger that is really only suitable for up to 55ah. It has lasted a year and recently has started letting me down. So I have bought a new 85 ah battery and put it in the van but never charged it as I assumed it already was. It lasted two hours. I have bought a new charger (8 amp) fit up to 120 ah and have put the battery on charge. Within two hours it was showing fully charged. I thought it would take 10 hours. Any thoughts?