Apple has quietly released a battery charger - and I must admit that I did not realise it was something special until I read the following :

The specs are what make this thing particularly interesting for low-power battery-powered devices:

each NiMH AA cell holds 1900 mAh charge (rumored to be rebranded Sanyo Eneloops)
the batteries are reported to retain at least 70% of their charge for 2 years
battery lifetime is reported as being at least 10 years (with recharges, of course)
the charger drops to 30 mW “vampire” power draw once the batteries are charged
To start with the latter: I’ve verified it. When charging, there’s a small yellow LED and it draws less than 4 watts. When done, the LED turns green, and power consumption drops to 0.18W. Then, after 6 hours, the LED goes off and the power consuption drops to… zero! At least on the very sensitive SBC-500 I used.

[From » New AA battery option Jee Labs]

Hm! As we have a AAA battery charger permanently plugged in this is interesting - I may have to go out an get one.