Hi Hitesh,
Thanks. The "earlier" model was the one that the APC Backup-UPS ES replaced. Unfortunately, I do not remember the model number.
In fact there was another APC 500 VA model even before that

, but that got withdrawn from the market because the input range it used to work in was very limited. That first model had some switches at the back to adjust the range (3 ranges I think).
BTW, you mentioned that you have availed the warranty. What went wrong with it and how long after you bought it?
DH