Thinkpads Forum

Hi all,

after a year of owning my T520, I noticed that the capacity of my 6-cell battery had dropped to 45.39Wh (from a design capacity of 56.16Wh). I decided to recalibrate it, and now it shows a capacity of 59.60Wh! What do you think: is it a really good battery, or is the calibration mechanism, presumably the way it measures power consumption, quite inaccurate?

By the way, am I going to notice increased battery life now? I.e. does it shut down when the battery is actually empty, or when it thinks it's empty?

Magic battery or crap calibration - likely neither.

Just let your battery run down to as close to zero in normal use and recharge again. The calibration system does not always give consistent results. until it has enough data collected over a few charge-and-discharge cycles, it will try to find the highest value and present that as the capacity.
A freshly charged battery could have a brief period where the charge contained is beyond design specs. that is normal. that spike in charge is quickly lost as the computer starts sucking power out of the cells. All batteries, unless supplemented by power control circuitry, have wildly varying voltage and amperes over a discharge cycle.

if the notebook gives you the runtime you want, and does not crap out on you suddenly, don't worry about the voltages and charge capacity. enjoy the computer and replace the battery when you feel the charge it holds is no longer sustainable.

oh, and if you spend a lot of time near a power outlet chaging your battery, use the excellent Thinkpad Battery managemant software that prevents 100% charge to extend battery life. I keep it 80% and 20%.

Thanks very much for the reply!

I guess my main concern (apart from curiosity) is if the notebook thinks there is more charge in the battery than there actually is, and it suddenly dies without getting a chance to go into hibernation. I do sometimes let it run completely dry when using it while travelling.

kona wrote: I guess my main concern (apart from curiosity) is if the notebook thinks there is more charge in the battery than there actually is, and it suddenly dies without getting a chance to go into hibernation. I do sometimes let it run completely dry when using it while travelling.

Just run it completely dry and see whether it dies or not.

kona wrote:Thanks very much for the reply!

I guess my main concern (apart from curiosity) is if the notebook thinks there is more charge in the battery than there actually is, and it suddenly dies without getting a chance to go into hibernation. I do sometimes let it run completely dry when using it while travelling.

Unless you have a spectacularly old Machine still running, I think you will be getting a fair warning (unless you disabled it!!) before the battery dies.

If you travel a lot and require your computer to be running for work, a new battery is a small investment for peace of mind.

Ok thanks. Yes an extra battery is the way to go.