alt Hacker NewsNiMH chemistry allows for safe overcharging though. If the chemistry allows for it, why not take advantage of it and have cheaper chargers?
The downside is that "save overcharging" only works at very low charging rates. That's why the double-charger designs all have 10+ hour charge times (mine actually has a 20-hour charge time).
But in practice? Its cheaper to buy 4 extra AA NiMH batteries to keep charged rather than upgrade to the faster chargers. So just keep some spares topped off and you should be fine.
Sure, but those NiMH have the same form factor by necessity, so it is confusing.
I would be surprised if the extra costs for the electronics for charging an extra cell are more than a few dollars.