Forgive me for the blatant obviousness of the answers but I’ve repeatedly demonstrated my moronitude here so what do you expect, right?
I have an old TI calculator with three worn-out AA-sized NiCads that I assume used to put out 1.2v each for a total of 3.6v. I want to replace them with three NiMHs, which should cause no problems. However, I do not have a 3.6v wall wart; the closest I have is 3.0v. Lemme see if I understand electricity (which I normally consider this side of magical) well enough: This adapter will still recharge the batteries, just a bit slower than the correct one, right? These batteries will still put out 1.2v each, right? They don’t much care the voltage coming in as long as it isn’t so high that it cooks them, except for that time thing, because I’d just be dumping electrons in, right?
The charging “curve” of NiCds and NiMHs are quite a bit different. In particular, overheating can be a problem for NiMHs. NiMH chargers detect how charged batteries are and adapts the charging rate to keep things “cool”. A little bit about this here.
In short: Wrong.
My advice: get a good “regular speed” NiMH charger. (Always avoid “rapid chargers”.)
Rather than log on to see if anybody answered I tried it using three AAA batteries because Rat Shack only carries a three-battery holder in AAA. After testing the calculator using carbon cells* I put in three brand-new, uncharged NiMHs** and plugged in the AC adapter. I tested it regularly and once the charge got high enough the calculator would switch on but kept acting stupid. After twelve hours with no improvement beyond “stupid” I removed one of the batteries and tested it. One of my guesses was RIGHT, believe it or not; it was putting out 1.2v and the whole pack 3.6v. So THERE, Mr Smarty Pants! However, the time factor was too high so I threw them in a proper charger and the calculator is chugging along happily. The next test is of battery life using dinky li’l AAAs (but 750mah ones) compared with my memories of how long one of these would work using what passed for NiCads in 1977 (about eight hours).
Yeah, carbon cells. They were cheap and good enough for experiments.
** - If I have as many AA NiMHs as I do why did I buy two packs of AA alkalines tonight? Because they were $2.50 for 24 and I don’t have to worry if they’re charged, that’s why!
However, the time factor was too high so I threw them in a proper charger and the calculator is chugging along happily. The next test is of battery life using dinky li’l AAAs (but 750mah ones) compared with my memories of how long one of these would work using what passed for NiCads in 1977 (about eight hours).