On 09/12/2016 11:24, john west wrote:
There's a lot of information about that if you keep a Laptop battery
charged between only 80% full and only 40% full, it will be servicable
over the years for four times as long.

Other information I find says it is the charging and discharging that
wears the battery out.

Both are true, but keeping it fully charged all the time kills it even
faster than cycling it through periodic discharge. It is bad to keep it
near either end of the spectrum for long periods of time. How hot the PC
gets plays a part too - and they generally run faster and hotter on
mains when all power saving features are typically disabled.

Charged and on mains supply is how I generally killed my portables - it
runs faster when on mains so it generally is unless I'm travelling.

Deep discharged and left for a long period of time will brick it into a
state where safety features will (should) prevent it ever working again.

The laptop i have (with a built in battery) is mainly used in one room,
so it is easy to keep it plugged in *all the time* to mains electricity.

Even so you should cycle the battery to 20% or lower and then recharge
at least once a month. I have killed plenty of laptop batteries on
continuous power. The newer chemistry is a bit more robust but in search
of ever greater energy density that margin gets eroded again.

Would it be better to prolong the life of the battery to keep it plugged
in all the time or to go for the 80% - 40% option. Thanks.

You need to cycle the battery every couple of weeks or so or the
chemistry will get stuck in a charged but forgotten how to discharge
state. That means when you do need to use it the remaining battery
capacity is a tiny fraction of its nominal rating. No problem if you can
always use it on mains power but a nuisance when travelling.

--
Regards,
Martin Brown