How to look after new laptop battery

[The Liquidator]

Just bought a new battery for my laptop. The 'puter is 6 years old but still works fine and at this point I figured if I can get another couple of years out of it for a £25 investment for a 7800mAh battery then the missus might be happy to see me buy a humdinger next time

Anyway, this is my 3rd battery for this machine. I ran with the first one bust for 2 years but bought a new one 18 months ago at the same time as my daughter (we both have Dells). Hers is still going okay (about 1.5 hours) whereas mine got down to 10% capacity (warning lights after a few seconds). I have put that down to the fact that I have tended to leave mine switched on, connected to the mains, for extended periods whereas she tends to run it on battery rather more - a little ironic.

From previous searches of the net on how best to look after a laptop battery the advice varied greatly and was confusing. One school of thought was that it should be fully discharged from time to time, whereas another was that doing so would wreck it. Others say charge when it's at 40% and ensure it's at that level when you store it. Any thoughts on a sensible regime I can employ to make sure this one will last as long as possible?

Thanks

[HalationEffect]

Wikipedia has some useful information about maximising Li-ion battery longevity:

Charging forms deposits inside the electrolyte that inhibit ion transport. Over time, the cell's capacity diminishes. The increase in internal resistance reduces the cell's ability to deliver current. This problem is more pronounced in high-current applications. The decrease means that older batteries do not charge as much as new ones (charging time required decreases proportionally).

High charge levels and elevated temperatures (whether from charging or ambient air) hasten capacity loss. Charging heat is caused by the carbon anode (typically replaced with lithium titanate which drastically reduces damage from charging, including expansion and other factors).

A Standard (Cobalt) Li-ion cell that is full most of the time at 25 °C (77 °F) irreversibly loses approximately 20% capacity per year. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively.

Prolonging battery pack life

Avoid deep discharge and instead charge more often between uses, the smaller the depth of discharge, the longer the battery will last.
Avoid storing the battery in full discharged state. As the battery will self-discharge over time, its voltage will gradually lower, and when it is depleted below the low-voltage threshold (2.4 to 2.9 V/cell, depending on chemistry) it cannot be charged anymore because the protection circuit (a type of electronic fuse) disables it.
Lithium-ion batteries should be kept cool; they may be stored in a refrigerator.
The rate of degradation of Lithium-ion batteries is strongly temperature-dependent; they degrade much faster if stored or used at higher temperatures.
The rate of degradation of Lithium-ion batteries is also related to battery charge level; they degrade much faster when at 100% charge, than at lower charges. Since batteries die if deep discharged (depleted) and since a battery has some self-discharge it is frequently recommended to store batteries at 40% charge level.

It seems that running a laptop on mains (while the battery is already fully charged) for long periods is just about the worst thing you can do when it comes to battery life. You're effectively 'storing' the battery at 100% charge in a warm environment.

*Note 1 - The summary in the first quote above reflects older designs that use carbon anode, metal oxide cathodes, and lithium salt in an organic solvent for the electrolyte.
*Note 2 - In the 2nd quote above, there is a question mark over the reliability of the source for all but the last statement.

[The Liquidator]

Thanks for that, very interesting.

[GreyGeek]

My old Sony VIAO VGN-FW140E had battery circuitry which prevented it from being charged over 80% and it would trigger a shutdown at 10%. It's four years old now and my son reports that it still runs for about 2.5 hours on that 70% of charge, just like it did when it was brand new.

Unfortunately, my new Acer 7739 pushes the charge to 100%. Like you, I tend to leave it plugged in all the time. In the last six months I've probably discharged it to 10-15% only a half-a-dozen times, so I don't expect this battery to last more than two years.