It's a little thing, but it pleases me because it avoids wasting some off-grid solar energy and helps ensure that we always have some AA/AAA cells charged up for gadgets...
I bought today a Maplin N42FK AA/AAA NiMH battery charger that can run from in a car (at 12V) and that has a timer and -deltaV cutoffs, ie should be safe to leave completely unattended with batteries in. It has a charge-state indicator which should help us know when the NiMH cells are full so that we can take them out and put them in out 'charged' box and rotate others in from out 'uncharged' set.
I have put this downstream of my LVD which was no longer being used for the laptop now that I am using the SheevaPlug for my server. The idea is that when the off-grid SLA battery is full-ish (and charging) then excess energy will be diverted to charging any NiMH cells in the charger. (Also the server will ramp up its consumption at its own chosen voltage thresholds as additional 'dump load'.)
This means that when there's excess off-grid solar energy available we can use a little of it recharging NiMH cells semi-automatically and when there are none there or they are charged then the server gets to use all that it can. In any case we waste less of what is available and 'free'!
Plus the charger came with some of the 'hybrid' NiMH cells, which have a lower-self discharge and that I want to try out.
Rgds
Damon