Cordless Drill Battery Maintenance

There seems to be quite a bit of interest in fixing cordless drills.  Even I have done one instructable on the topic ( which I will put first here! otherwise no particular order ).  Most of the fixes involve the battery: some replace it, some soup it up.  This guide will help you find many of the instructables in one place.   If you have an instructable on this topic and I have missed it please let me know.  If you would rather junk the battery and add a cord see:  There are other things you can do with your cordless drill, more guides coming, one covers running the drill without the battery:  Cordless Drill Repair - Add a Cord
Drill Resurrection with New Batteries for Cheap style
This adapts an old drill to accept inexpensive Harbor Freight batteries.
Rebuild an 18v drill pack for 15 bucks! style
Extract cells from a cheap replacement battery to rebuild a "original" battery.
Converting Cordless To Lithium Li-Po style
Change the battery type for better performance?
Makerspace Power Tool Upgrade: NiMh to Lithium Iron Phosphate style
Expensive, heavy, but perhaps still useful.
Free Drill powered by a laptop battery style
Here is a really different and quick approach. How can using duck tape be bad?