Batteries: Ni-CD -vs- Ni-MH

[TheSlashFiveTourer]

A question for our electronic experts here on The Forum if I may....

Is there a major problem involved if I use an 3-year old Radio Shack NiCad battery charger to charge up a set of the "new and improved" Ni-MH (metal hydride) batteries? I notice there is a small rocker switch on my Shack charger showing "Ni-CD" - "Ni-MH." What happens to the new Ni-MH (hydride) batteries ("AA") if I leave the switch in the "Ni-CD" position while they're charging??

Considering the price, are these things really that much better than a good set of NiCad's??

Thanks for any assistance.

[BRADFORDBENN]

The charging speed is different between NiCD and NiMH. So you can damage/degrade a NiMH set using the NiCD setting.

The main difference between NiCD and NiMH is the memory effect. NiCD will not recharge fully if they are not drained fully. They will only be usable for the amount of charge you provided. A better way to explain it: If you drain a NiCD to 25% left and then charge it back to 100%, the battery will only have 75% of its original capacity available. It gets worse and worse as time goes on.

NiMH are designed specifically to avoid this problem so that you can charge them whenever convinient without getting a memory. They are worth the extra money, really.

[CGARR]

I have been using NiMH batteries in cameras, remotes, radios, and GPSs for the last 2+ years. They do cost more, but they are definately worth the money if you use them. I have yet to see any of my batteries start to degrade in any way. I figure they paid for themselves and the chargers in less than a year.

Benn is right about the charge rate, and you don't want to mix NiCD and NiMH in the wrong chargers. I have tried NiCD batteries in the past, don't even bother, the do develop a memory, mine were shot in less than a year. Another nice toy to have is a charger that will charge off a 12V electrical system. So you can recharge on the road.

I think if you try the NiMH out you will find that they work out very well. Good luck.

[dancogan]

I learned about what is commonly called the "memory effect" of Nicads. It really isn't so much memory, as it is the need to totally discharge nicad packs before charging them. Failure to fully discharge them leads to imbalance in the battery pack, which ultimately prevents the pack from accepting a full charge. (You have to remember that most nicad batteries are actually packs of individual nicad cells wired together in series, with each cell producing approximately 1.2 volts, as opposed to the 1.5 volts of a typical AAA, AA or similar battery.) When I flew electric airplanes (of the RC variety-not full scale) we would run the pack down fully after landing with either the engine, or by attaching a dummy load such as an automotive tail light bulb. Most people don't run their nicads down completely before charging and ultimately end up with battery packs that are out of balance and won't accept a full charge.

The problem with the new rechargeable replacements, as I understand it, is that they self discharge even faster than nicads. Nicads lose their stored charge at a rate of at least 1%/day, if I remember correctly. Hope this helps some.

[LORAZEPAM]

I use the NiMh hatteries and they are a real improvement over NiCad batteries. I have a spare set, and charge them up and rotate the batteries in my gps and cameras. I have a one hour charger, and combined with the extra set means I never run out of juice.