According to HerHusband :
It only takes about 10-15 minutes to refill our pressure tank. And, if the
power goes out and we conserve our water usage, the pressure tank can
supply all the water we need for hours. A generator seems like a hassle to
install, maintain, and operate just for running a pump for 15 minutes.

If the power is out long enough that the batteries would go dead, we'll
have other issues than just the water supply.

When you price out a 2500W inverter[+] which may only be able to fire your
pump up for one and a half 15 minute sessions, then you'll have an "issue"
with your pulse rate ;-)

You'll probably have better luck with a gas generator - keep it at the
house, and feed the pump from there.

Not practical. The house is too far away from the pump and the pump has
it's own power connection UPSTREAM of the house.

I was thinking that may be part of this...

[+] more so even than gas generators (which have rotational inertia to help
with startup surges), you _really_ have to oversize the inverter for the
startup surge on a motor.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.