Is there any point removing a fully charged battery from a laptop on the mains?

Kernel_Sanders

When you use a laptop without a battery, the current obviously bypasses the part of the circuit into which the battery fits. But is this still the case when a fully charged battery is inserted, therefore maintaining its longevity?

John_Gray

I would have said that if the battery is fully charged there's no point for the laptop charging circuits trying to put any more charge in it.

Interestingly, I had an ancient Advent laptop which would only work if you removed the battery! (I do not have a high opinion of Advent laptops.)

spannerzone

I think many batteries fail due to the heat in the laptop cooking the battery, rather than the battery being over charged (which shouldn't really happen these days)

Some people remove the battery if only using on mains to prevent it cooking and prematurely failing, the downside is that the battery is a perfect and convenient UPS should the power fail it immedietly kicks in and keeps the laptop running.

thescouselander

If you are going to remove the battery to keep it good it needs to be around 50% charged (assuming it is the newer lithium based type). Storing the battery fully charged isn't a good idea as it will degrade.

Kernel_Sanders

John_Gray wrote: »

I would have said that if the battery is fully charged there's no point for the laptop charging circuits trying to put any more charge in it.

Unless it is constantly replacing the power being taking from the battery.

John_Gray wrote: »

Interestingly, I had an ancient Advent laptop which would only work if you removed the battery! (I do not have a high opinion of Advent laptops.)

Surely your experience with the Advent proves that the mains circuit
is physically blocked whenever the battery is in position (I'm presuming the battery was so old it could no longer accept a charge).

esuhl

John_Gray wrote: »

I would have said that if the battery is fully charged there's no point for the laptop charging circuits trying to put any more charge in it.

Lithium Ion batteries are liable to explode if overcharged (or re-charged after the charge drops too low), so there will be circuitry to stop the circuits trying to increase the charge beyond a certain point.

spannerzone wrote: »

I think many batteries fail due to the heat in the laptop cooking the battery, rather than the battery being over charged (which shouldn't really happen these days)

thescouselander wrote: »

If you are going to remove the battery to keep it good it needs to be around 50% charged (assuming it is the newer lithium based type). Storing the battery fully charged isn't a good idea as it will degrade.

Apparently heat does reduce the lifespan of a Li-ion battery, as does the charge-level. If you store the cells at 100% charge at 25C, they'll degrade around ten times faster than at 40% charge at 0C (see link below).

Ideally you'd want to store the battery with as low a charge as possible, but it will gradually lose charge over time, and if it becomes undercharged the laptop circuitry will prevent it from being re-charged (making it useless).

I use 18650 cells (the same ones used to make laptop batteries) in high-powered bike lights and keep them in the fridge, but I'm not sure whether there would be more complex electronics in a laptop battery that might not like any dampness. I'd imagine it would be fine if you wrapped it in a plastic bag...

This webpage has a fair bit more info if you're interested:
Battery University: How to prolong lithium-based batteries

spannerzone

Do you find keeping the batteries cooler makes them last longer or increase the lifespan?

esuhl

spannerzone wrote: »

Do you find keeping the batteries cooler makes them last longer or increase the lifespan?

Batteries will all degrade over time. By that, I mean that chemical changes inside will gradually reduce the amount of charge they can hold. So, while my laptop lasted for 2hrs on a full battery when it was new, that's now been reduced to 45mins.

That's not the same as saying that you can get more charge out of a fully charged cell by keeping it cool. If I remember rightly, there's an optimum temperature (~20C?) for usefully discharging a cell.

So, if you're actually using the battery, keep it at room temperature, and try to minimise the time that you charge/discharge it.

If you want to store the battery unused, it's best to reduce the charge (but not by too much) and the temperature.

There is so much apparently-reliable information on the web about this that I haven't conducted any experiments myself to confirm this.

Hope that helps...