Instructables
Picture of Refit cordless screwdriver with dead battery
Had a 9v screwdriver that would no longer take a charge. Was going to rebuild battery pack but it was custom fit for the handle (pita to replicate). I had a bunch  of RC car batteries left over from days gone by so I put the two together. From two things I had no use for sprung forth a handy tool.
To make this work you'll need a battery pack. I used a 7.2 volt one I had laying around. You can pick them up on ebay for about7 or 8 bucks but you will need a charger. If like mine the charger circuit was shot. Yeah maybe I could have fixed that, but was above my pay grade. Mine was a 9 volt driver but the 7.2 battery works great.
 
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Step 1: Open it up

Picture of Open it up
I split it open and removed the battery pack. I laid the new pack in and cut one side of the handle as far as the current circuity would allow.

Step 2: Put it back together

Picture of Put it back together
I put the driver back together as the wires I would splice were long enough to do this work outside the driver. I have a bunch of these batteries so I planned on swapping them out. With this in mind I put a new connector (TAMIYA fitting) left over from Remote car days. Later I decided to just tape it in and charge it in place after trying bungees and other methods of holding the battery.  I taped it in with what is known as rescue tape. I buy generic tape off amazon in packets like the one above the drill in the picture. Stuff is awesome for all kinds of uses. I have other drivers but this one fit in places the others won't and I like making trash useful again.