NiMH Charging techniques, memory

[Corndogg]

My Dive Rite mini wreck HID is down to about a 1 hour burn time these days so I charge it after every dive.  I have always been lead to believe that NiMH batteries had no memory and you could treat them however I wanted until I came across this:

Battery Life
Nickel Metal Hydride (NiMH) batteries are rechargeable and can be recharged for hundreds of cycles. Your battery life will depend on how you properly care for your battery. Gerbing's does not offer any warranty on the lifespan of your NiMH battery.

To break in a new battery properly, we recommend charging and discharging the battery fully 4 to 6 times to enable the battery to reach its full rated capacity.

NiMH batteries have no memory effect, but the memory is held in the charger. Over a series of charges, the charger remembers the charge capacity required to bring the battery to a full charge. If you run your battery for only 1 hour, then recharge, the memory will adjust to provide 1 hour of charge to recharge. This is not enough! To prevent this, condition your battery and charger by charging the battery for 10 hours and then draining the battery until your heated product no longer is providing heat. Be sure to always disconnect the battery from your product when it stops providing heat.

To increase the longevity of your batteries, don't leave them dormant for extended periods of time. We recommend that you completely charge and discharge at least every 2 to 3 weeks. Batteries left idle for extended periods of time self-discharge at a rate of 2% per day. Just remember to charge your batteries again before use.

I clipped this off of this site while researching my heater setup: 

I'm going to run the battery through several complete cycles and then do a burn test and then post the results.

[eric myers]

I would be interested in your results but I caution you don't do anything outside of what is reccomended in the directions that came with the light.

I just got this light as well and I have be using it in the kitchen sink to drain it for 5 -1o minutes then charging until it says it is charged.

I read through all the instructions very thoroughly and the cycling 4-6 times is supposed to only be when you are breaking it in for the first time from brand new.

One thing the directions say is AVOID draining the battery all the way, if you have done this on more than one occassion in the past it could explain why your battery is maybe starting to go.

If you get a chance you may wish to speak with a Dive Rite Rep. Start with a Dive Rite dealer and get contact information from there.

Please post your results.

Good luck!

[Dan G]

Everthing I have found suggests avoiding fully discharging NiMH batteries. I didn't bother trying to find out much information about charging them, until I had a dive light battery pack explode on the bench during a charge after a complete discharge. It completely ruined two cells.

there's a lot of reading in this, but it seems to match most other stuff I have read about them.

[Inspirationdiver]

I'd also have to strongly discourage fully discharging the NiMh batteries. 

This is in fact one of the disadvantages of HID lights when compared to halogens.  With the HIDs, it will burn at full strength until the battery is completely dead.  With halogens, the intensity will decrease as the battery becomes discharged, allowing you to shut it off before damaging the battery pack.

I'd also add that NiMh battery life is determined by the number of times it's charged and discharged.  While they don't technically develop a memory, they do gradually lose their overall capacity the more times they are cycled.