NiCd falling behind

Starting in the 1950's, NiCd batteries were the only game in town for a reasonable rechargeable battery that could replace non-rechargeable AA, AAA, C, D, and 9V size batteries. And they were made in other sizes too if that's what was needed for an embedded application. In fact, more NiCd cells were made for embedded applications than as AA, AAA, C, D, and 9V battery replacements.

What's an embedded application?
Embedded applications are when a cell or battery is housed inside the device that is being powered. This would include battery packs that come inside a plastic housing. Frequently a battery pack will include the cells and electronics for battery management. Replacing these cells is a great deal more difficult than just buying a new set at the local store, opening an access plate and popping it in.

NIMH is the new kid in town
So NiCd ruled the roost for about 30 years until NiMH came along in the 1980's, The extra capacity per charge in the same size NiMH, about double that of NiCd, allowed that chemistry to take over. This was especially easy since the charging protocol of NiMH was so similar to that of NiCd so one didn't always have to get a new charger for the new chemistry and charger designs just needed a little tweaking. And NiMH did not contain as much heavy metal content so it was deemed less hazardous.

But embedded applications did not really fall in line and use NiMH because it's overall life, about 1/2 as long as NiCd, was especially difficult if one had to break a case open or unsolder the cells to replace them. NiCd is simply more robust so the embedded market stuck with it. In fact, power tools have gone straight from NiCd to Li-Ion as their power source skipping a generation of NiMH power tool batteries entirely, for the most part.

What does the future hold?
But that brings up the next threat to NiCd. Almost all power tools have switched over to Li-Ion. The only consistent place one can find NiCd these days is embedded applications where the battery pack is not removable.

NiCd is still relatively cheap. It's still the most robust of the common rechargeable chemistries. But as supply drops, prices may rise. And when prices rise enough, we may see the end of NiCd.