With the old lead acid battery I was reasonably clued up. But as we went to NiCad then NiMh and others the whole thing changed. If we look at a lap top battery there is complex electronics in the battery to stop over charging, even the AA cell today can have electronics
to control charging built into the cell. The problem with the AAA and AA cells is they have been around for a long time, so you have the full range from NiCad to lithium which all fit our devices, there was a one point a rechargeable 1.5 volt alkaline as well at the more normal 1.2 to 1.3 volt cells.
I know I had a phone in my mothers bedroom which was regularly knocked off the cradle, it would not charge when I came to it, I swapped one battery and it started to charge, then swapped back and it continued to charge, however we would get pips sounding from the base. Over some two months it has started to behave itself and now works A1. I will guess there is some anti-reverse fitting protection which to start with stopped it recharging but unless one does some reverse engineering you really have no idea what is in the cell.
With the old NiCad cell it was stored discharged after manufacture, however once activated it could grow crystals which would internally short it out, so you then had to keep it charged so if a crystal did grow it would be burnt off, there were a few methods used to try and remove crystals however today that is no longer possible as we have no idea of the electronics included.
So with AA cells I find them marked between 700 mAh to 2.8 Ah there may be even bigger ones now. The old charger was designed for around 1.2 Ah and it had a timer which switched off after a set time. So fit a set of 2.8 Ah cells and as long as the cells are not fully discharged all works A1, as far as the charger knows the cell is between zero and full but in fact the cell is between 60% and 100%. Once it goes below 60% the charger will switch off before fully charged. Not fully recharging will in the long term damage the cell. However if only made flat once in a couple of months, then each time it is used and put back on charge it will gain a little extra, so will return to fully charged.
So my camera with a special battery not a problem, the manufacturer knows what is in the battery, Nikon did a firmware upgrade on some of their cameras which stopped you using 3rd party batteries. But in your phone the manufacturer does not have a clue what battery is fitted, so if they use a very low trickle charge they are reasonable safe, but put any system to limit the recharge the software in battery and software in phone may not work together.
So to basics four ways to charge rechargeable AA and AAA batteries.
1) Trickle charge no control.
2) Higher rate of charge with timer.
3) Higher rate of charge with temperature sensor.
4) Delta-V
I am not sure if Delta V will work with modern batteries, idea was at a constant current the voltage will raise to a peak then drop again, the charger detected the voltage was falling again and auto switched off once detected.
The temperature is still a reasonable method, again constant current, while electrical energy is turned into chemical energy there is very little heat, but once that is complete the temperature will raise. I still use that with a general AA battery charger, if battery is warm, then assume fully charged.
