Powerex Maha MH-C9000 Charger
In 2002 I researched and bought a good battery charger called the Maha C-204F. It only does AAA and AA batteries, but it charges them fairly slowly which means they are charged more fully and with less heat (damaging) than the fast chargers that you get at regular stores. 
I had to order the Maha (billed as "the mother of all chargers") from Thomas Distributing because they aren't easy to find. It worked great for a couple of years before one side of it went bad and I could only charge two batteries at a time instead of four. Eventually I bought another one just like it from Thomas in 2006. I burned out its AC adapter in Ireland when I plugged it in to a 220 socket, but I had the old adapter, so no problem.
After my dealings with flashlights lately, I also learned some about batteries and particularly NiMH rechargeable batteries. I have been using them for a long time and even got some Sanyo Eneloops in 2008 to use in my calculator because they hold 85% of their charge after year whereas regular NiMH batteries can easily lose 10% per month. After three months of no use you really need to recharge regular NiMH batteries because if they get too low it can damage them. I got some pretty high capacity NiMH batteries to go with Susan's camera a few years ago and they were toast after maybe a year. They just never held a charge very well. Part of that may have been not adequately breaking them in by charging them and then using them (not all the way down) a few times.
So anyway, I have all these old marginal batteries including the 8 generic green batteries that came with my Archos. Those batteries still work, but they're not great. That's okay, really, because NiMH batteries aren't supposed to last forever. Some of the batteries I have, including the ones I took back from Susan, get very hot when they are charged or the charger has a hard time recognizing them. I threw away some Energizer NiMH's because the Maha just refused to deal with them.
One of the problems with the Maha is that it applies the same charging cycle to two batteries at the same time. If one of the batteries is bad, this can mess things up and you'd never really know what was going on. It is better to get a charger that charges each battery separately. However I don't have one of those.
There are two good chargers out there that can analyze the actual capacity of a NiMH battery and can also recondition them. People on Amazon report bringing otherwise useless batteries back to nearly original condition. The two chargers are the La Crosse BC-900 and the Powerex Maha MH-C9000. The BC-900 is less expensive, smaller in size, and comes with 4 AA batteries and 4 AAA batteries (as well as plastic adapters that make AA batteries the size of a C or D battery so you can use AA's in the place of those bigger batteries). The MH-C9000 is at least twice as big, doesn't come with freebies, but gets better reviews at Candlepower Forums (from a surprising number of people who own both of the units). Both are harder to use than just dropping batteries in and waiting for the green light to come on. They have LCD displays telling you a battery's voltage, capacity, and time elapsed and can charge and discharge batteries at various rates to help recondition them. Both have very long conditioning cycles that can take 36 hours for a set of 4 batteries.
There is a detailed review at Amazon that favors the BC-900, but there is an even longer review at Candlepower that favors the MH-C9000. I debated whether I even needed one of these things. For the price of the cheaper $40 BC-900 I could buy all new batteries and throw away all of my misbehaving ones. I may have to do this anyway because both units can tell you that a battery is shot (and often do for older batteries) and at that point it should just be recycled.
But after a lot of internal debate, curiosity and the desire for an ever more powerful gadget convinced me to get the Maha charger. It should arrive by the end of the week. While the BC-900 was a better value, the free batteries it came with weren't of much value since I wanted Eneloops and already have a lot of conventional NiMHs.
Once I get a chance to try reconditioning some batteries I will let you know how it goes. Once I work my way through my whole collection, I will be happy to recondition batteries in the family. Although it is large, I could take it on vacation and let people use it down there. Once a battery is reconditioned I don't think there is any harm in continuing to use it in a regular charger.
Also I found what looks like a pretty good basic charger by Duracell that meets the minimum criteria of charging cells individually and being a smart charger that charges slower and cuts off based on when the battery is full rather than just after a certain amount of time. It is CEF23DX2 and has the kind of neat feature of having a USB power port that runs off of the charger's AC adapter, the car adapter (not included with this model which also includes 2 AA Duraloops), or by charged batteries sitting in the charger. The similar CEF23DX4N includes 2 AA, 2 AAA, and the car adapter. Be careful because Duracell also sells dumb chargers and 15-minute chargers that shouldn't be used.
Conclusion: After getting the charger and working with all of my batteries, here is my conclusion: This is a good charger. It does a couple of key things: 1. lets you discharge a battery to find out its actual capacity, and 2. lets you charge a battery at the appropriate rate for its capacity. The break-in cycle (which one reviewer said was worth the price all by itself) and applying multiple cycles to a battery don't seem to make much difference. Admittedly, the instructions only recommend the break-in cycle if you have a battery that has sat on the shelf for a while and self-discharged and I didn't have any of those. But I never realized any significant gains after using a break-in cycle that I wouldn't have gotten by just discharging and charging the cell. Therefore I don't see how this charger has any big advantage over the LaCrosse charger since that model does the same two primary things, costs less, and comes with 8 batteries. Negative reviews based on the complexity of the Maha's interface seem groundless: If you have fairly new batteries (that don't require charging currents less than the default) you can just insert them, walk away, and it will charge them. Doing more advanced stuff is easier than setting a digital alarm clock. It asks you for a value and you use the up and down arrows to get what you want and press Enter.
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