On Sunday, May 27, 2012 21:37:49, Robert Holtzman wrote: > For the record, I'm running a Lenovo T420i with a 6 cell battery. > > In the past I've been told that it's bad practice to run a laptop on AC > with the battery installed because it would cause reduced battery > capacity. That's correct most of the time. > This raises two questions. First, is it true that laptop > batteries don't have overcharge protection, and second, how many cycles > is a battery like mine good for? Most laptop batteries today are Lithium-Ion type. Lithium-Ion batteries get damaged when they are at either extreme in terms of charge. At 100% charge the Lithium-Ion mixture can crystalize and the battery looses capacity. At near 0% a Lithium-Ion battery is at risk of exploding, so there is an internal safety circuit to permanently disable the battery if the battery charge is brought too low. The best storage charge level for Lithium-Ion is 40%. The best option for Thinkpads is to install the packages 'tp-smapi-source' and 'tp-smapi-dkms', the latter which willl build the tp-smapi kernel module. [Read the docs that come with tp-smapi-source, which will explain more about Lithium-Ion battery thresholds.] This allows setting the low and high charge thresholds via /etc/sysfs.conf [after the 'sysfsutils' package has been installed] with rules such as: devices/platform/smapi/BAT0/start_charge_thresh = 30 devices/platform/smapi/BAT0/stop_charge_thresh = 91 With rules such as the above, the laptop can be on the charger and the battery plugged in and sitting at 40% and NOT be charging. This means that the laptop can safely be on the charger all the time, and yet not damage the battery. I'd like to think there is a similar utility to do this for non-Thinkpad hardware, but I haven't looked for it much. Final note on battery tech: Nickel-Metal-Hydride (NiMh) and Nickel-Cadmium (NiCad) batteries both exhibit an effect called "memory", so they should always be fully discharged followed by a full charge. So be sure to know the type of battery your laptop is using. -- Chris -- Chris Knadle Chris.Knadle@coredump.us GPG Key: 4096R/0x1E759A726A9FDD74
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