Overcharging alternator

[Terry]

A mate phoned me yesterday and asked for a jump start.
When I got there I tested the battery and found it at 1.24v. He said he must have left the lights on overnight.

Anyway I jumpstarted and it ran at 14.2v on idle. We noticed when revved to 5krpm and over the dash warning lights started coming on and the battery was showing 16v.
So it looks like the alternator needs changing, This morning he's text me and told me the battery is dead again.

Is it likely the alternator overcharging has knackered the battery as well?

[Dom]

Yup

Even a few deep discharges can totally kill a battery. I'd replace both to be on the safe side and test the new alternator output for the first hour or so to make sure you don't kill the new battery..

[Terry]

Cheers Dom,

I've no idea how long it's been overcharging for so it could well have been a while. I bet he won't be happy with the cost lol. It's only discharged twice but i'll change the battery as well.

[Tathan]

I had an alternator with a knackered regulator that was overcharging a battery, also killed the battery (obviously). Managed to get halfords to exchange it though as a faulty battery, naughty me. So possibly try that depending on age of battery.

[Terry]

He's only had the car 9 months and battery was on when purchased. I think it may even be original.
My mate can sort me a brand new battery for £30 so i'll stick that on.

[Vinci]

Beware of cheap overcooking batteries, the acid will be quite destructive to your car! Here in the Netherlands the Kwikfit garages have batteries called Coldax and they are notorious for overcooking!! Not the alternator to blame, they even do that under normal circumstances.

Charge voltage is best kept at max 14,5V and NEVER over 15V.

Lead acid batteries can deliver monstrous currents, but they are VERY vulnerable in some respects. Also some damaging actions will not immediately reveal, but will just make them live a short life (will reveal when using a charger that can monitor the total discharge capacity) Actually discharging under 10V is to be rendered certain death, it will definitely show in lowered capacity. Under 8V is an immediate throw away, not even worth looking at again.

Some examples of good treatment are nog discharging them under 12V too much, too often or too long. Also they like being topped up constantly with a tiny current, hence the solar battery protection panels available WILL enhance battery life. Then off course a battery low voltage switch off protection will be very useful. NEVER charge them faster than the manufacturer states in the datasheets!!!!! Charging them too fast will cause a very damaging chemical reaction inside the battery, which is also VERY DANGEROUS because hydrogen gas will be generated and that's very explosive gas as you might know!! A safe limit that any lead acid battery will be able to live with is 1/10 the capacity as charge current. So for a 50 amp battery the charge rate at 5A will always work well (will top it up in 10 hours)

There are different types of lead acid batteries, some can be discharged very far or charged fast. These however are extremely expensive and most often used for fork lifts and such, not in cars...