Last year, I added a bilge pump to the window well which was powered by a couple of 6V lantern batteries. This worked - until the batteries died.
So - I decided to up my power source to an AGM (absorbed glass mat) Lead Acid battery which gets charged via a solar cell.
DISCLAIMER: Be careful when using tools - protect your eyes - think twice before doing anything. With batteries, you can't unplug them - they're always 'hot' - watch where you put your tools - avoid possibly shorting out the terminals. Keep the protective terminal covers on the battery until you actually connect it to your circuit, and when you do, make sure a fuse is the first thing to get connected. Batteries can be dangerous - they can explode - leak acid.
Step 1: The Bilge Pump
The bilge pump is designed for small boats to expel water within their hauls and keep them afloat, it's not an industrial pump by any means. The accompanying switch is a small float switch which closes the circuit once the water level is at a certain height.