Charging a battery

[R13hard]

My friend has left his car battery on charge today by accident!

The charger is a cheap mains charger with no auto cut out!?

We were wondering if the battery will be alright for another 6 hours as he will not be able to get home. The battery has been charging since 7am. Usually takes around 4 hours to fully charge.

[neverlandandy]

i remember years ago in the winter we would take the battery out and charge it all night dont know how these newer batteries would stand up to that

[67688c]

Should be okay... I assume its probably a self venting battery, and if not the vent caps have been removed while charging. 6hrs shouild be ok.

The charge to the battery gradually reduces anyway as it become charged, this is because a car batteries resistance is far lower when discharged, and gradually increases as it becomes charged. Thats how these auto cutoff and so called smart chargers know when to cut off or reduce the charge to a trickle.

[Gsi3.2]

unless it's boiling up it will be fine to leave it on longer than you wanted to.. even with no autocut off..

[Phatty]

Batteries are endothermic on charge, so will absorb energy in the form of heat... Charging for extended periods of time will cause the battery to 'boil' which wastes energy and in turn shortens the life of the batteries.

Overcharging can cause degradation and buckling of the plates. In the process some active material is forced off the plates and drops down to the bottom of the battery.

Only if this occurs frequently will you have a problem - the eventual result is a build up of a bridge between the plates which in turn can cause a possible short across the plates. This leads to the destruction of a cell.

The outcome is a reduced battery life and reduced performance and capacity of the battery.

So, all in all, you won't really see any difference in performance etc as it's only a one-off - and it won't explode either which is a bonus

[Caterman]

Nice answer Baz So you do learn something in work then

[Phatty]

Nice answer Baz So you do learn something in work then

can you tell i work with batteries

[Duncan]

Nice answer Baz So you do learn something in work then

Nah, he's just been doing some Googling - http://www.bigginhill.co.uk/batteries.htm

A reasonable rule of thumb is that you should aim to charge the batteries only when they are between 70% and 40% discharged. If you charge them then they are only lightly discharged i.e. less than 40% you will end up boiling them unnecessarily which wastes energy in the form of heat and gassed off hydrogen and in turn shortens the life of the batteries. In effect the batteries are being overcharged which can cause degradation and buckling of the plates. In the process some active material is forced off the plates and drops down to the bottom of the battery. If this occurs frequently the eventual result is a build up of a bridge between the plates which in turn can cause a possible short across the plates. This situation leads to the destruction of a cell which then reduces the capacity of the battery.

[Phatty]

yup - it's something we print off in work and give to newbies