I'll try the UPS, can I get that from Radio Shack maybe?
No doubt you can get one there, but realize your trying to run a compressor motor off a little battery, it won't last more than a few minutes unless it's a very large one.* Better to hook up an inverter to your house batteries, but beware that some digital controls won't like anything but a true sine wave inverter.* Our modified sine wave inverter cooked two control boards on our de-humidifier before I realized the problem.* Now I just run it off shore power and check on it as often as possible.*
If you install a true sine wave inverter things should be fine, but if the power is off for a long time, it will completely discharge the batteries.* When power is restored the inverter will recharge the batteries, but it may draw enough current on the AC side that additional other loads (like the de-humidifier) will blow the shore power circuit breaker.* The ability to regulate the charging current will allow you to reduce the AC draw though.
Ultimately, there's no substitute for checking on the boat as often as possible........Arctic Traveller
Trawler training at www.arctictraveller.com