I was riding my Big Bear up a long steep hill today, and the power suddenly cut out half way up the hill and the kingmeter went dead, and I couldn't get it to work again and I had to cycle the rest of the trip unpowered. The problem occurred about six miles into the ride and the battery had been fully charged before the trip and was working fine until this happened. I have a second battery for the bike, and I rode the bike with the second battery later in the day and it worked fine. I charged the batteries afterwards and they both charged as normal, going from red to green when they had finished charging. I then tested the faulty battery again and it still didn't work. The faulty battery had been working fine before the problem occurred, and it did not appear to be nearing the end of its life. The battery is not under guarantee any more and so I would have to pay to get it fixed. I make a lot of long trips and I need two batteries rather than just one, and I really do need for this battery to work again. Could anyone tell me what the problem is likely to be? Thanks for any help you can give me.