[Wiltshire] OT - Power tool batteries

[Ben]

I would like to say that in general you should use a NiCD charger to 
charge NiMH batteries.

I have to say that this was initially a feeling I had but a quick web 
search turned up this

 >>Can I use my older NiCD battery charger to charge my NiMH batteries?
 >>
 >>No, you can use a newer NiMH charger to charge your old NiCD 
batteries but you should
 >>not try to charge NiMH batteries with a NiCD charger. Here's why: 
NiMH and NiCD
 >>batteries are chemically very similar and when both are fully charged 
the battery
 >>voltage will start to drop. The NiMH voltage drop is much more subtle 
and more
 >>difficult to detect. NiMH chargers usually have an over temperature 
sensor and
 >>shutoff to prevent overcharge as well as a more sensitive voltage 
drop detector
 >>where NiCD chargers usually only use the voltage drop to determine 
when to stop
 >>charging. If you charge NiMH batteries in a NiCD charger it will 
probably miss the
 >>voltage drop and keep right on charging causing the batteries to 
overheat.
 >>Overcharge and overheating NiMH batteries can damage them internally and
 >>reduce battery life.

 From http://www.starbatteries.com/chargerfaqs1.html

David it sounds from your, primitive if effective :D, temperature 
monitoring that you may have got away with it but that does not mean in 
general you can charge NiMH batteries in a NiCD charger.

Cheers
Ben

David Fletcher wrote:
> Simon brought along a decidedly dangerous looking power tool battery/charger 
> on Monday night i.e. both had grossly overheated and partly melted the 
> plastic casing.
>
> What I've got is two Bosch cordless drill/driver tools, one nearly new, the 
> other several years old. The battery supplied with the old one died, and the 
> charger supplied with it is pretty pathetic. So, for less than the price of a 
> decent charger and new battery, I bought a new tool, taking the same 14.4V O 
> pack as the old one, and provided with a decent charger that rapid charges 
> then switches to trickle when it knows the battery is about full.
>
> Having been warned about ebay batteries, I took a look. What I've now got is 
> what looks like a genuine (but you probably can't tell) Bosch battery pack 
> built with NiMH cells rather than the NiCd ones provided with the new drill, 
> claimed to be 2.6AH capacity in the same size case as the 1.5AH battery 
> supplied with the new drill.
>
> Put it on charge tonight, the charger warmed up slightly, the battery stayed 
> cool while the LED flashed to indicate fast charging. When I noticed the LED 
> had stopped flashing the battery was nicely warm but not hot. Left it for a 
> couple of hours, then the charger was still warm but the battery had cooled. 
> I guess it's working OK.
>
> If anybody is interested, the new tool I bought is a PSR 14,4-2, including a 
> model number AL1411DV charger. It's nice that the battery pack is compatible 
> with the old tool.
>
> Dave
>
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