About 1:20 am it started to rain and I was getting ready to go to bed

1:30 am the power goes out and it is down pouring rain

Now I need to stay up to make sure the sump pump well doesn't over flow

Stay alert as much as you can.

Got lucky the power is back on at 1:50 am

I am running on battery power.
since September 2003.

don't know much about sump pumps... my house is about 2' off the ground... but a small inverter style gen set would be on my short list, if the sump's power consumption was in the 2kW area...I have a 3500W Honda traditional gen set, but recently bought as 2500/2000 Predator for portable use.... on sale for $350... haven't had much time on it, but brochure claims 5 hour or so run time on standby....runs fairly quiet compared to the 3500... YMMV

Power outages are routine in our area.   Our sump pump runs quite a bit as well.   A couple of years ago we put in 20KW Generac to assist with the outages.   We have been really happy with it.   Power goes out, the Generac starts, and the lights come back on.  

Last Labor Day weekend the wife and I went for a walk.   The day was beautiful, the sun was shining, a light breeze was blowing.   When we got back from our walk we noticed that the generator was running.    Logged on to the power company's website and see that three whole towns are out of power.    Interesting but not really an issue for us.   About 9PM I decide to take a drive to see what I can see.    I drive slowly, car windows open, and I watch and listen.    It was DARK out.   Every house was dark.   I can hear a generator running here and there and see dim lights here and there but I drive a couple of miles into town.   The place is dark.   Stop lights aren't working.   It was erie dark.   I drive back a different route.   When I turn the corner onto our street I see our house.   It is lit up like an F'scking Christmas tree.    Even the front lights are on.   "ummm.....   guys......    we need to tone this down a bit!!!!!!"

2Hut8

OpSec.... tag you're it.[:)

Yep.   In a BIG way......

2Hut8

People on boats have what they call "BILGE Pumps" they are the same equipment as a sump pump, but really important.
 It is fairly common on small boats to run the bilge pumps on batteries, usually 8D size batteries which weigh around 130 pounds, and  can run pumps and radios for a couple days, if necessary.  If your sump pump is critical infrastructure, you may consider using a DC model, and running it full time from a small battery bank, with a maintenance charger.

Big difference is that a sump can pump with quite a bit of head.  Bilge pumps, unless you go for ship sized where power isn't an issue, tend to only be good for a few feet of head (think bass/sail boat) where they just have to get the water up a foot or two above the water line to spit it out the side.  

Read up on some of the home made battery backups people have made from 2 to 4 bateries of various types.

Not being home or being asleep and not noticing the power went out would be things that could cause you to have problems with the sump pump.

Plus battery thing can be used for other stuff as well.

I expect there is a commercial version as well and yeah you have to size it for your sump setup but overall it should not cost that much and would be nice to have for piece of mind.  No I did not use the wrong piece.

I remember seeing sump pumps in Lowes or Home Depot that ran on both 120VAC and 12VDC. They are made to run off a 12V car battery when main power fails. The pump control box should have a battery charger circuit too. Check them out.