According to HerHusband :
Does anyone make a UPS (uninteruptable power supply) powerful enough to run
a 1/2 HP - 240V submersible water pump?

Many manufacturers make UPSes that big, the problem being you need a _big_
one, and the price will be appalling. And when sitting outside during
the bad weather you need it for, battery life and runtime will be a
serious issue.

[Ie: lead-acid batteries lose a _lot_ of capacity below, say, -15C]

A 1/2HP water pump takes about 800W to run. About 2500W to start, but I'd
not think of using a generator smaller than 3500W.

You also have to be concerned about waveforms. The less expensive UPS's
generate square wave. Which induction motors such as your pump don't like.

You're looking at several thousand dollars worth of UPS. Which, chances
are, won't be working (or have much capacity) when you need it.

I just don't think UPSes are practical for running induction motors in a
residential situation. A gas generator is much more cost-effective, and
capable of extended operation. Which is what you need to recharge a 250gal
pressure tank anyway.

I'm working with a similar situation, and am (slowly) constructing a battery
backup system to provide small amounts of power during a power failure.
The _critical_ thing we need is to ensure that the sump keeps going. So,
I'm stringing in a 12V bilge pump that'll be able to push about 500GPH. With
the battery I've chosen, it's good for 20 hours of continuous run. Plus
a bit of 12V lighting, and a 400W inverter to supply AC for some small things
(like the small blower on the wood stove).

That's _all_ we need for a 48 hour outage.

If we ever go further, it'll be a 5500W (or more) gasoline generator - diesel
if I luck out and find one cheap.

You'll probably have better luck with a gas generator - keep it at the house,
and feed the pump from there. Or, maybe, you can wire in a 12V pump.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.