Hi, Silvio; tudo bem? (are you well?)
This is not a complete reference, but I believe it is a good starting point; I would appreciate extra comments, suggestions and mostly corrections.
Based on what I know and have heard about, NiCad's and NiMH have different behavior when recharging cycles are the issue. AFAIK, NiCad's should never be used till their charge (ddp and load current) is nearly exhausted, meaning they should not be connected to the load for longer than it's recharging demand. Otherwise there are some "dangers" (not destructive) related to the so called "memória de carga" (I do not know the name of it in English, but this is the effect observed when charging cycles happen too frequently, mostly before proper time, and the batteries get "used to" that behavior) observed in the NiCad's. Based on these facts, allowing the batteries to discharge till the equipment signals this fact is the procedure I'm adopting so far. If I am using the equipment (calculator, printer, any NiCad operated portable) and it signals Low Battery condition, I promptly connect it to the AC adapter and let it connected for as long as stated in its manual/guide. I avoid using the charger for periods in time longer than the necessary to fully recharge the batteries. I read that NiMH batteries are a bit different, because they do not have the "memory" effect and may be recovered when nearly exhausted.
The only equipment I saw that has a different charging procedure is the 9114B disk drive, but it uses an acid-composed battery (like automotive batteries) and this is another story: they better be floating around their operating voltage for as long as they can be.
Hope this helps. And please, guys, add whatever needed to complete this information, O.K.?
Luiz C. Vieira