Overcharging NiMH Battery

[JasonH20]

Lets just say a "friend" of mine hypothetically suddenly just realized whilst trying to fall asleep that he had accidently left his battery pack plugged in ALL DAY at work, and left without unplugging it. This "friend" promptly jumped in his car and sped off to work to save his battery. All said and done, his 4.5AmpHr HiMH battery pack (standard Terkel issue) charged from 7am until about 11pm. :11: He was just using the cheapo charger that came with the battery pack.

So my <cough> friend has asked me to ask on this board what if any damage he might have done to the battery? The battery is obviously pretty warm, but there were no flames or smoke to speak of. Is the battery still usable? Is it trash? Something inbetween.

Boy, I hope I never do something stupid like that myself. :xeye:

PS, can someone post some links to those fancy chargers for our dive light batteries?

Thanks,
Jason

 

[miketsp]

It's difficult to comment without more data.
It really depends on the charger. You say it was the one that came with the battery pack.
What would the standard charge time be for this charger and this pack?
How many connections are there between the pack and the charger?
If there are just two, positive and negative, then it depends whether the charger has voltage limiting.
If there are more than two connections then it is probable that there is a thermistor built into the battery pack to detect over-charging (over-temperature) and limit the charge current.
The easiest way to find out is to test the dive-light by turning it on, dumping it into a bucket of water and timing it to see if the battery has degraded.

 

[MXGratefulDiver]

Lets just say a "friend" of mine hypothetically suddenly just realized whilst trying to fall asleep that he had accidently left his battery pack plugged in ALL DAY at work, and left without unplugging it. This "friend" promptly jumped in his car and sped off to work to save his battery. All said and done, his 4.5AmpHr HiMH battery pack (standard Terkel issue) charged from 7am until about 11pm. :11: He was just using the cheapo charger that came with the battery pack.

So my <cough> friend has asked me to ask on this board what if any damage he might have done to the battery? The battery is obviously pretty warm, but there were no flames or smoke to speak of. Is the battery still usable? Is it trash? Something inbetween.

Boy, I hope I never do something stupid like that myself. :xeye:

PS, can someone post some links to those fancy chargers for our dive light batteries?

Thanks,
Jason

Tell your "friend" that it's unlikely that any damage was done ...

With a standard charger, a basic household timer will eliminate the problem. Costs about $5. You simply plug the timer into the wall socket, plug the charger into the timer, set the number of hours you want the battery to charge, and come back within 24 hours to unplug it.

However, if you really want a fancy charger, this is the one that I use ... costs about $75.

http://www.thomas-distributing.com/mh-c777plus.htm

PS - you will also need to purchase a pair of Anderson connectors (can be found at most electrical supply outlets) and solder them into the pigtail that comes with the charger.

... Bob (Grateful Diver)