Recently I had a problem with my 800VA UPS – its internal rechargeable batteries was not working out as it had in the beginning. So instead of having new internal batteries, I went ahead and bought external rechargeable batteries – though these were made for car, I assumed that they will also work out for UPS – shop owner also told me that would be ok – and its working out fine. I am getting about 2 hours of backup which is more than enough for me. They are sealed maintenance free rechargeable batteries – at first I thought of having unsealed rechargeable battery but then went against it because I keep them in my living room – so I don’t want to mess up my room any further (its already a mess)..