[user18]

My friend has an AA/AAA battery charger. If I were to connect a C battery holder to the + and - terminals, would it be able to charge a C battery? Could this work? The multi-type charges are quite a bit more expensive. I'm wondering if it as easy as adding a battery connector to the chain.

 

[DanPash]

Yes, you could charge a c cell. It would just take longer to charge.

 

[balou]

well, it depends on the charger design. there are chargers who just charge with 1/10 of the assumed mAh of the battery - those need about 14 hours (mathematically 10, but batteries aren't perfect) on batteries specified for them, and linearily longer for higher capacity batteries.
Then there are timer based chargers - they will charge with 2/10C for 7h or so (just an example). They won't really work with higher capacity batteries, or you have to reinsert the battery after the first charge.
Then there are delta peak chargers - they look for a voltage bump and shut off if it occurs. they should work without problems. there are also chargers with thermal shutdown - NiMH get hot if they are overcharged. Those chargers should work aswell