Originally Posted by
duke_of_hazard
Thanks for all the replies, I take it the answer to my question below is no.
Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?
I'll try to answer accurately: No, I dont believe it is possible.
A nickel-metal-hydride charger must respond to a voltage drop of 8-16mV per cell. Making the charger too sensitive may terminate the fast charge halfway through the charge due to voltage fluctuations and electrical noise. Most of today's nickel-metal-hydride chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge.
Note: that refers to intelligent chargers
There are several ways a charger can detect when a battery is fully charged and a decent charger will often use several at the same time.
If your charger has a temperature monitor it might cut off before the healthy battery is too badly damaged.
If your charger detects the delta peak (very unlikely when charging 2 batteries in parallel) I would say you have no chance of not damaging the healthy battery.
Sorry, a cheap charger is a cheap charger.