Sometimes you can select a power tool with a specific battery type. A good example is cordless power tools. Drills can be bought using NiCd, NiMH or Li-Ion batteries.
Recommended by toolmonger.com and myself:
Buy Li-Ion tools if you can afford it, otherwise buy NiCd. NiCds are supposed to have higher capacity for heavy duty power tools than NiMHs.
I actually own one of each, both made by Makita. The Li-Ion is nice because I can leave it for a long time and it still retains its charge. The NiCd will lose it charge in a few days and have to be recharged.
The manual for my Makita Li-Ion drill says:
Charge the battery before completely discharged.
Change the battery when the drill starts to slow down.
Never charge a fully charged battery. Overcharging.
Let a hot battery cool to room temperature before cooling.
My recommendations Li-Ion power tools:
Do not discharge all the way.
Do not run in hot environment (if possible).
My NiCd drill and batteries are probably 8 or so years old so the batteries don’t last very long. I don't use it very often so I had to recharge a battery before I could use it.
I ran both batteries down a couple of times (see picture) by wrapping some house wiring around the switch and letting it discharge. After the batteries cooled off, I recharged them. They seem to run a little better and don't self discharge as much.
I also tried discharging my cousins Skil drill (see picture) a couple of times and saw a big improvement in run time.
I also stuck one of my NiCds in the freezer. Freezing NiCds is controversial. Several sites, including some manufacturers say you shouldn't do this. Some websites suggest doing this to get rid of memory problems. I tried this but saw no improvements.
Now most websites that do recommend freezing say you should put them in a plastic bag so that they won't absorb moisture. I agree.
Now many websites say freezing will greatly reduce the self discharge problem. This is the main reason I tried this.
PROBLEM: Most websites recommend that you take the battery out of the freezer and let it come back to room temperature. Now, for me this defeats the purpose as I just want to use my drill immediately. If I still have to wait a couple of hours, I might as well just put in on the charger instead of freezing it.
SOLUTION: Well, I decided to try it right out of the freezer. It seemed to work fine. Now I haven't experimented much with this and cannot recommend it. But, at your own risk, you might try freezing your battery for immediate use. Make sure the battery is dry.
Power tool battery replacements:
Lots of stores and websites sell replacement batteries for power tools. Some places like Batteries Plus will actually replace the batteries in a power tool battery pack. Most of these battery packs have multiple cells in them. Remember the standard NiCd battery is 1.2V so to get a 12 volt battery pack, there will probably be 10 cells in it.
Now I had a Hitachi cordless drill with two battery packs. They wouldn't hold a charge so I opened them up (see picture). Some of the cells appeared to be dead. I decided to take some battery cells from one pack and put them in the other one to try to make one good battery pack.
Failed: The first problem is that the cells are connected with those metal strips that are mechanically attached to the cell. Well, I was able to solder to them. But the biggest problem is that replacing a couple of 'bad' cells, just caused some others to fail. After doing some research on battery packs, this is understandable.
Recommendation: If you want to replace cells in a battery pack, replace all of them with new ones with the same capacity and close to the original battery capacity. You might think higher capacity battery cells would last longer but it depends on if the battery charger can fully charge them.
Please recycle all old batteries. My local Home Depot, Ace hardware and Batteries Plus will recycle batteries.
My recommendations NiCd power tools:
Once every month or so, discharge all the way and recharge.
Do not leave on charger once it's charged.
Remove from tool if not being used for a while (Don’t know if this really helps and I don’t do this).
Now if you don't use your power tool that often, you will probably have to recharge it before use.
You might try the freeze method; see caveats above or just stick them in a bag and put them in your refrigerator.