I have a ThinkPad 600t laptop (IBM) that uses a Li-ion battery pack. The pack is rated at 10.8 volts 4400 mAh

Recently it started to not hold much of a charge.

So I opened it up to see which 'cell' was bad on the assumption that I might be able to replace that one cell with a cell from another Li-ion battery pack I have (which is also bad). I figure that out of the 12 total cells, six for each battery pack, I am bound to find six that are good.

Well, I tested the voltage on each cell and they are all good!??($*# Current levels are high as well (i.e. they don't drain down fast when I test for load).

I'm puzzled.....I just assumed one or more of the cells would be bad. Apparently they are not. Hmmmm. The voltage at the terminals measure 12.1 volts (I don't see how...)

Anyone know how I might proceed? Why is the laptop telling me that I can only get a 46% charge and then when I unplug from the charger, it drains within 5 minutes. I'm puzzled regarding these 'smart' batteries.

Reassemble the battery and check with an application like Mobilemeter [link below] to check your battery's wear level. The battery's age and frequent use affects the capacity over time, but if your battery is still within warranty, you might want to check its policies.

http://www.softpedia.com/get/System/System-Info/MobileMeter.shtml there are other sites that carry this app.

Once you run MobileMeter, go into the system tray and right click on its icon, then options, then the "Battery Information" tab. Wear level is in the percentage as well as other capacity info on the battery.

Hope this helps.

Just measuring the voltage under no load won't find all battery faults. They need to be loaded down a little to see a voltage drop.

- Pete

I thought that is what I did when I tested under 'current' conditions ...

Sorry, missed that.

- Pete

IIRC, Li-ion batteries have an average useful life of about three years. You can replace the bad cells, but you may not be adding a lot of life to your battery if they're from another "dead" pack.

i agree with ozmoid. laptop batteries don't last very long... plus their so expensive to replace with a new one. i think your lucky to get 3 good years out of them.

I can't find the specific article I was looking for , but the same basic info is on wikipedia:A unique drawback of the Li-ion battery is that its life span is dependent upon aging from time of manufacturing (shelf life) regardless of whether it was charged, and not just on the number of charge/discharge cycles. So an older battery will not last as long as a new battery due solely to its age, unlike other batteries. This drawback is not widely publicized.[4]

At a 100% charge level, a typical Li-ion laptop battery that is full most of the time at 25 degrees Celsius or 77 degrees Fahrenheit, will irreversibly lose approximately 20% capacity per year. However, a battery stored inside a poorly ventilated laptop may be subject to a prolonged exposure to much higher temperatures than 25 °C, which will significantly shorten its life. The capacity loss begins from the time the battery was manufactured, and occurs even when the battery is unused. Different storage temperatures produce different loss results: 6% loss at 0 °C/32 °F, 20% at 25 °C/77 °F, and 35% at 40 °C/104 °F. When stored at 40% charge level, these figures are reduced to 2%, 4%, 15% at 0, 25 and 40 degrees Celsius respectively.[5]

The advice I got on Li-ion was "Charge early, charge often." But the aging factor is what I was trying to remember, that's why the old packs are likely not to be worth the effort to replace from another old pack - they're all dying anyway.

Full entry here (http://en.wikipedia.org/wiki/Lithium_ion_battery).