Laptop batteries

[Dave2002]

In the past I have found that laptop batteries don't last for ever, and become poor after a few years.
Modern laptops are probably better, but will still most likely have batteries which wear out over time.

Is it better to cycle the batteries - i.e. let them almost run down, then connect the laptop to the charger, or to keep a laptop as topped up as possible? Maybe it's just random these days, and decline is inevitable whatever one does.

I tend to keep my MacBook plugged in when at home, but sometimes, for various reasons it gets unplugged, or the cable falls off and it runs down. I can also, and do, take it out without the charger for meetings if I only need it for a few hours and usually it holds up for long enough, but would not make it through a whole day.

[Don Petter]

I did some mild research a year or two ago when I had to replace the battery in this Dell laptop (theoretical battery price about the same as a new modest laptop, but I found a cheaper one on Amazon which has served well).

It seems that if you are going to run for long periods on the mains it's bad for the battery and best to take it out. Apart from the fag of anyone bothering to do this, the battery on this machine physically incorporates one of the four feet, so it's not practical. I did moot removing the electrical connections on the dead battery and then using this as a dummy with foot while in the house, but never got round to it!

[MrGongGong]

Battery technology has come on a lot in the last few years
but if you use your machine a lot they will start to deteriorate fairly quickly
on my Macbook i'm on my second one which after a year and a half is starting to fade
but I do use it all the time and every day and often with bus powered soundcards etc

It's false economy to buy a cheap "equivalent" though
when I did that for a Sony laptop a few years ago the "new" one lasted 3 months before only holding about 20 mins charge

[johnb]

The best charging regime depends on the type of battery. NiCd and NiMH batteries can have a "memory" effect where repeated partial charging can reduce their charging capacity. The obvious problem is that it is almost impossible, with normal laptop use, to always fully charge the battery then always to discharge it to a low level - so compromises have to be made. When the battery capacity is reduced due to the memory effect I seem to remember that one way of restoring the battery to its charging capacity is to fully charge it and then let it fully run down and repeat that for three cycles. (My old Thinkpad has a battery 'restore' option which does just this, though for only one cycle.) Having said that, all batteries lose charging capacity over time, whatever you do, and the effect of battery "restore" procedure is modest in my experience.

However, lithium-ion polymer batteries (as used in iPads etc) behave very differently. They do not have a memory effect and it can harm these batteries to let them fully discharge (similarly charging to 100% can harm them as well - but this will usually be protected by the computer or device). I've seen recommendations to maintain the charge between 40% and 80%, with a monthly full charge/discharge to 5%. Once again practical considerations mean compromises have to be made.

[Eine Alpensinfonie]

However, lithium-ion polymer batteries (as used in iPads etc) behave very differently. They do not have a memory effect and it can harm these batteries to let them fully discharge (similarly charging to 100% can harm them as well - but this will usually be protected by the computer or device). I've seen recommendations to maintain the charge between 40% and 80%, with a monthly full charge/discharge to 5%. Once again practical considerations mean compromises have to be made.

So this begs the question of why NiCd and NiMH batteries are used at all.

My work laptop battery eventually would hold no charge at all, and would not function unless the battery was removed completely, and it remain that way for two more years until I handed it back.

[Bryn]

So this begs the question of why NiCd and NiMH batteries are used at all.

My work laptop battery eventually would hold no charge at all, and would not function unless the battery was removed completely, and it remain that way for two more years until I handed it back.

NiCads are basically obsolete. NiMHs do not exhibit anything like the memory effect of NiCads, which needed frequent controlled discharges to extend their lives. In the past few years NiMHs with slightly lower capacity, but which hold their charge much better, have come onto the market. Look out for descriptions such as Stay-charged, etc. Neither NiMHs nor NiCads find use powering laptops these days.

[Dave2002]

NiCads are basically obsolete. NiMHs do not exhibit anything like the memory effect of NiCads, which needed frequent controlled discharges to extend their lives. In the past few years NiMHs with slightly lower capacity, but which hold their charge much better, have come onto the market. Look out for descriptions such as Stay-charged, etc. Neither NiMHs nor NiCads find use powering laptops these days.

I recently was investigating batteries for another purpose - to run an amplifier in order to cut out any mains problems. I found this page which has a very interesting table showing the energy density of a large number of different types of battery - http://en.wikipedia.org/wiki/Rechargeable_battery