OK, so, I have an APC UPS Pro 1000 (aka 1kva). So, the battery has just died on it, and I am thinking I will just connect up a deep cycle marine battery. However, I am wondering a few things.

Does the onboard computer have a memory of how much voltage is in the battery, or does it actually take direct readings? So, in other words, if I hook up a battery to the UPS, will I get the full battery power, or will I be limited to the same capacity of the current battery?

Also, any recs on the casing? The one I have now won't fit a large deep cycle marine battery...

I was also considering hooking up 2 or more batteries in a parallel circuitry. Does anyone foresee any concerns with this?

Any and all tips and recs appreciated.