recommendations for UPS purchase?

[Brian Williams]

Scot, you wrote:”…

If the battery dies after three years and the rest of the unit still 
works, I plan to hack them to use a standard marine deep cycle battery 
that will cost about as much as replacing the UPS and will provide a 
much longer backup time.”

Be cautious here. You may find that the battery is ‘floating’ and that neither the negative nor the positive of the battery grounds to the UPS unit (via the ground pin of the cord). 

The voltage from either of the battery terminals to ground may be significant (presenting a health hazard (i.e. electrical shock) or present a risk of fire).

How do I know this? I did what you proposed. A shocking discovery.

The batteries within the UPS are usually easily replaceable and are a common stock item at electric supply shops. Perhaps it's wise to verify battery availability when selecting your UPS.

Good luck,, Brian