Alvin, Cambridge, Mass asked:
Is it really better to let a battery completely run down before charging it?
We put this to Patrick Palmer, University of Cambridge, Department of Engineering:
This is a very good question that exercises me most mornings after I've cleaned my teeth and I don't know whether to put my toothbrush back in its holder and charge it or whether to just leave it on the side. There is some truth in the fact that the nickel cadmium battery which is the light-weight one occasionally needs to be helped by being deep-discharged. Most of the time just discharging it 20% and recharging it is okay but it needs to be reset once every month or so, something like that. The lithium battery that’s popular in telephones is also light-weight. These, however, do need considerable care. That’s why you find lithium batteries in mobile phones and in laptop computers. Their charging and recharging has to be monitored very carefully. They have protection circuits in them usually. So occasionally it probably is a good idea to let your laptop run flat. Do that occasionally because that allows the computer to recalibrate itself and be up and running for the future. The other main type of battery is your lead acid battery in the car. In fact we know very well that lead acid batteries can work very well if they’re just kept basically topped up the whole time. Care is required and occasional deep-discharge of nickel cadmium, and for that matter probably nickel metal hydride – probably less often – just by using it in the equipment ‘til it’s flat is probably not a bad idea.
It all depends, on the battery, what sort of battery it is, and what charger you're using and what device is discharging the battery.
http://www.batteryuniversity.com/ Pumblechook, Wed, 15th Oct 2008
I stumbled across a datasheet for Li-Ion/Li-polymer batteries recently and it recommended that if you're not going to use them for a while, the Li-based batteries should optimally be left at 40% charged! New batteries would also be supplied 40% charged - hence why new mobiles now have some life in them before the first charge.
I have just been reading about batteries in a mag.
The brother of a friend of mine used to race model (electric) cars. These were powered by ni-cads. I recall coming in one evening to find my friend's brother connecting a massive spotlight to some of his battery packs. I asked him what he was doing and he replied that he'd got a big race the next day and that he was fully discharging the ni-cads before overnight charge in order to improve the capacity for the race.
The one thing I am struggling to comprehend with this area is the actual chemical basis for these battery effects. Why are lithium cells so fussy, and why do NiCads have nightmares if you don't deep discharge them?
I can't vouch for the veracity of this page -- but it does address NiCad memory:
There are conflicting ideas on how the different types of battery should be charged etc..
Lead Acid accumulators don't like being discharged more than 50%, I've heard. lyner, Sat, 3rd Jan 2009
Yes for nickel cadmium cells and batteries