Hi just got a 2nd hand bike for my wife which rides well but seem to have a battery issue. Sits at 20% (not flashing) after several hours so suspect its sat uncharged fully for some time. Checked on Halfords site but saying new battery not currently avaialble on line which seems odd but seeing others on ebay but dont know which are compatable if indeed any are. Any advice for a newbe to ebikes would be appreciated