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.

I think those suckers take readings of the voltage, though if it's higher or lower than the stock battery it may freak out and not properly condition power / recharge if there is a failure. Not really a memory issue, but how the hardware is on the board.

It's worth a shot if you have a spare laying around. Worst thing that can happen is that it fails... well that or explode. I suppose exploding would be the worst.

If it doesn't work, call a battery store and check how much a new cell at that range would cost.

I think the worst would be if it turns into Venom and foils all your crime-fighting plans.

I think I need to get out more.

As I understand it, 'smart' batteries cannot measure the charge currently contained within themselves (there is something awful about that sentence, but I think its OK).

The charge is measured as it enters and leaves the battery. When you recalibrate a battery by charging it full, discharging fully, then charging fully again this resets the 'charge-o-meter' to 100%.
Thats how Apple laptop batteries work at any rate. If yours is as smart, it should be able to recalibrate itself to a new battery. I confess I don't know much about the variations of currents and voltages used to recharge batteries and their associated tolerances. I would guess that a nasty miscalculation of this is the sort of thing that could make a battery explode.
3rd party batteries with higher capacities seem to work fine with Apple PMUs, SMCs etc. As far as I know, the electronics are identical to Apple batteries but the actual cells are upgraded.

hmm, so...

Not really sure about this, I def am not looking to have an exploding battery... I don't think thats going to be the case, but at any rate, I wanna be sure that this will work.

Anyone with any experience on this?

You can use the battery but use a automotive 20amp fuse on the battery.

20 amps is the standard current for the electrical in your home?

20A is a reasonable and safe amount of power for pretty much any appliance(s) you might need. In the UK, you don't often see fuses over 13A in appliances, I think they go to 30A in domestic fuseboxes.

For 12volts most fuses are 7.5, 10, 20 and 30 amps. If you use something that needs a crap load of amps or wattage then 40 or 50 amp fuses are needed. For examples my carputer power supply uses a 10amp fuse and I also modded my gaming PC's power supply to use 10 amps for 12 volts and 7.5 amps for 5 volts for the DC outputs. My car amp uses a 40amp fuse for the main power but the amp has a 15 amp fuse. So if theres a power surge the 15 will blow first and if it effects my main power the 40amp will blow.

Your UPS is nothing more then a power inverter with a battery. It turns 12 volts DC into 120 volts AC. When it's plugged into the wall it's going into two way. Straight power to the device and also into a battery charger keeping the battery charged.

The UPS should have a voltage regulator so you shouldn't really even need a fuse but I would add one just for as a safety. Last thing you need is to test it or wait for a power outage and too many amps end up into the PC or even into the battery.

yea, so, I am wondering, I am probably draining some decent power here...

Mac Pro w/ 3HDs
4 LCD's
Cable Modem/Router
Backup 2-HD RAID Kit
MacBook
Printer
100Watt Lamp
iSub/iSticks

There are some other smaller things, but those will be the major power suckers...

So, you are recommending a 20A on the lead from the UPS to the battery? On the positive terminal, right?

If I run a couple in parallel, would you put one on each positive lead?