At what voltage do you need to charge NIMH AA & AAA batteries?

My DMM is on the way & I plan to top off my Lithium cells at 3.8 volts, when they are down to about 30%, but at what voltage is it best to top off NiMH AA & AAA batteries?
I have always run them until the light wont stay on high any more so is that just as good?

Testing nimh with a DMM won't tell you much. Good cells will have a resting voltage of around 1.2V when the are in the range of 0-100% charged. It is usually higher when at 100% depending on the cell.

Nimh need to be charged when their voltage sags to ~1.0-0.9V under load. Even that depends on how much load is on the cell.

Just charge the cells whenever you get a chance after they have been used. Draining every last bit of energy out of them is just going to shorten the life of the cells and make you mad when your light is dead when you need it just cause you were trying to get everything the cell has to give.

I use to monitor my batterys with my DMM while charging but my new hobby charger does it for me now and is quite accurate. My ni-mh batterys usually have arround 1.45v. fresh off the charger and after resting a while settle to arround 1.41 to 1.42v.
Billy