NiCd vs NiMH batteries
Both are 1.2 V rechargeables. NiMH roughly doubles the capacity and drops the cadmium; NiCd keeps an edge only in high-current, cold and abuse tolerance.
NiMH replaced NiCd for almost everything. Both give 1.2 volts and both recharge, but NiMH holds roughly twice the energy in the same cell and contains no cadmium, which is toxic and heavily restricted. NiCd's remaining advantages are real but narrow: it copes with very high current draw, deep cold and long periods of neglect. Unless you are replacing cells in older power tools or emergency lighting that specify it, buy NiMH.
- Verdict:
- NiMH, unless you specifically need what NiCd does
Side by side
| Specification | NiCd | NiMH |
|---|---|---|
| Nominal voltage | 1.2 V | 1.2 V |
| Capacity (AA) | 600–1000 mAh | 1900–2500 mAh |
| Cycles | 1000+ | 500–1000+ |
| Memory effect | Pronounced | Slight at most |
| Toxicity | Cadmium, restricted | No heavy metals of concern |
| Cold and high current | Excellent | Good |
| Availability | Declining | Everywhere |
The memory effect was real
NiCd cells repeatedly part-discharged could appear to lose capacity, which is where the habit of fully draining rechargeables came from. NiMH barely shows it, and modern advice is the opposite: top up whenever convenient and avoid deep discharges.
Cadmium is why it went
Cadmium is toxic and its use in consumer batteries is restricted across much of the world. That, more than performance, is what ended NiCd's run — and it is why spent NiCd cells must go to proper recycling rather than a bin.
Where it hangs on
Emergency lighting, older cordless tools and some aviation and industrial kit still specify NiCd for its tolerance of high current and long float charging. Substituting NiMH there is not automatically safe; follow the equipment's requirement.
Check before you swap. Batteries with similar dimensions are not always interchangeable. Always verify voltage, chemistry and the requirements printed in your device manual before fitting a replacement.