battery charger speed question

The faster charger simply charges with a higher current than the slower charger. There are potential problems with charging at higher currents. When charging at a low rate, there is little danger of overheating the batteries, or causing damaging internal pressure increases. When you charge with a higher current, these dangers can exist. The trick is to know when to terminate the charging cycle. NiMH batteries exhibit a subtle "flattening" or slight negative delta-V of the cell voltage when they reach full charge (much more subtle than the negative delta-V of NiCDs). Decent chargers will look for this "signature" to terminate the charging cycle. If you don't do this, you run the risk of overcharging, which can damage the cells (high temperature, pressure, etc.). The importance of proper charge termination increases dramatically as you increase the charging current (decrease the charging time). The slow 12+ hour chargers are essentially trickle type chargers that cause little or no cell damage with overcharging, so no charge termination is usually necessary.

I know that when I was buying a NiMH battery for my cell phone, they made a big issue that you had to buy a battery with the chip included to control charging rates. Because the charging rate was controlled by the battery, the $12 car charger was affordable.

I don't know how that works for generic NiMH batteries like AA or such. Is the chip still "in the battery"? If not, then "better understanding" of the chemistry and the charging profile, and perhaps a more expensive chip to allow handling more power as it passes through the control chip.

I expect that your cell phone battery is Lithium Ion, not Nickel Metal Hydride.

Lithium Ion batteries are very fussy about how they are treated, and will apparently explode if mistreated, so they are not available as individual cells on the consumer market. Even companies that will rebuild battery packs of other technologies often won't touch LiI.

No - NiMH batteries don't need a chip in the battery - the AA "batteries" are really single cells. (A battery _should_ refer to two or more cells connected together (usually in series.))

"More heat generated in the battery" and "a bigger transformer is required" are the obvious drawbacks. I don't know how it affects total charge or lifetime.

I would guess "more expensive" and maybe "a better understanding of NiMH chemistry" are (some of) the differences.

I don't understand the question. The "FAST CHARGER" charges the batteries faster. What seems to be the problem? ;-)

Actually, it's probably just a matter of the available charge current, or it could be that sometime between 2000 and 2003 somebody implemented a faster charging profile algorithm.

Hope This Helps! Rich

Well now, that's a little known piece of information that is nice to know! Thanks for the info.