Odd TK41 Behavior

So recently my kids night light bulb had went out. I havent had the time to pick up a new bulb so I figured it would be a good time to really make use of my TK41. Ive been leaving it on the lowest mode throughout the night time hours. Its been working wonderfully. After a few days of use I noticed the light was a lot dimmer than the normal low mode. I tried switching modes but no go. I knew I wouldnt get the claimed 240 hours on low since they tested using 2500 mah cells and Im using 2000 mah eneloops, but this did seem a little short. I shrugged it off anyways.

Then last night I recharged the batteries and stuck them in. I accidentally left the light on all night and throughout the day. I came home and noticed it real dim again, so dim you can look at the LED with no harm. Under the circumstances it was very possible my kids may have switched modes while I wasnt home and it ran the cells down as expected. I doubt that though, they know not to touch my toys :twothumbs. Either way, I decided to take some readings.

I pulled out my DMM and tested the voltage. I tested a few randomly and everything was checking out. The cells I tested were pretty damn depleted. Still confused, I decided to check ALL the cells. Thats when I noticed, some of the cells were full! . In a few of the series, one cell out of the two were still testing around 1.2v.

Anyone know what could be wrong? Im guessing it could very well be my crappy *** charger. Its one of these http://www.riteaidonlinestore.com/energizer-recharge-e2-compact-charger-2-aa-and-2-aaa/qxp206204. I did notice that the charger seemed to claim they were done fairly fast so Im guessing that has something to do with it. I didnt think to take readings when they came off the charger. I just got home from a long day so I dont have the energy to recharge the batteries and take readings just yet but any suggestions would be appreciated.

Ill probably recharge them tomorrow and see how they look like. I may have very well answered my own question

It's common in devices that I've used that have NiMN cells in series, that one cell gets rundown while the others still put out nearly full voltage, although they have lost half or more of their capacity. I've also found that my cells seem to get a better charge in those chargers if I charge them in pairs, rather than four at a time.

Hmm that's wierd. I have used my TK41 three times now on turbo mode only pretty much. I use eneloops and recently bought the Powerex Imedion AA 2400 mah LSD cells. They last about 15 minutes longer than the Eneloops do (Imedion's not broken in yet?) on turbo mode in the TK41 and don't cost much more. But I have the Maha 800s charger which charges 8 AA cells at the same time. I always notice that, while there are some variances, all of the cells are depleted close to each other after turbo mode is not selectable anymore. I can tell because the charger I use shows me the power level of each battery on the LCD readout. Maybe it's the charger?

The only way to know is doing individual charge and discharge tests on the batteries. The Maha C-9000 is your friend.

Chargers that "charge 2 or 4" batteries at a time should be avoided. Not only the charge process is suboptimal, but if one or more of your batteries have failed you'll never know.

Nap.

Yeah, like Napalm said. You could do with a Maha MH-C9000. Also, if you have a multi-AA device, and one or two of the cells are faulty or not as good as the others, it can ruin the batteries, because it reverses the current in the lowest charged cells once they go below a certain voltage. It won't be a problem with the TK41, and in fact the eneloops might be recoverable if they're treated right... Or one or two of them might be ruined.
Wikipedia states:

A complete discharge of a cell until it goes into polarity reversal can cause permanent damage to the cell. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the good cells will start to drive the disc.harged cell in reverse, which can cause permanent damage to that cell. Some cameras, GPS receivers and PDAs detect the safe end-of-discharge voltage of the parallel cells and auto-shutdown, but devices like flashlights and some toys do not.

Click to expand...

(I've been on a steep battery learning curve just lately!... My MH-C9000 is ordered but yet to arrive at time of typing this... So I'm by no means an expert.)