How do you know when the battery is kaput?

[Pip1968]

As per title. I did change the OEM battery for a similar power and size unit namely a Bosch S4 075 - 60Ah/540 cca (and only £50.88 from Eurocarparts) but when I looked at the little 'window' on the BMW battery it still seemed to be green. It had been on trickle charge.

Now I know it was probably due to be changed due to age anyway but how can you tell that the battery is kaput aside from dim lights (not experienced), unable to crank the car (it was flat after being in with BMW for a while) and the battery warning light (not seen). Can I measure the voltage across the terminals or is this only when on the car - ???

I am just wondering if it is my alternator failing and not the battery.

Pip

[LeinsCSL]

What charger have you got Pip? Think my CTek MXS 5.0 can tell if the battery is fooked and won't hold charge properly, as it won't go onto the later charging stages

[Pip1968]

It is a trickle charger CTEK or similar but I am not sure which. It just has an led for voltage and one for charging - low/full I think.

I am away so cannot pop into the garage for a check up.

Pip

[LeinsCSL]

That sounds like a different one, as the 5.0 has a row of LEDs and a reconditioning function

[Monkey]

Hi Pip,

Unfortunately there is no real way to check a battery without a battery tester. We would only really replace a battery if the customer was experiencing power issues.

The battery warning on the dash will only really come on with an alternator fault.

You can do a quick check of your alternator;

Using a multimeter put the leads across the battery terminals. Set it to 20v if not automatic. It should read somewhere around 12v with no ignition on. Then start the car it should increase to around 13v. Then switch on all electrical loads - lights, blower, a/c & heated rear window. What you are now looking for is this voltage to remain steady at the very least. Depending on the state of the battery it may increase up to around 14v. If the voltage starts to drop, and cannot be maintained its an indication the alternator is failing.

If this is found to be ok, you have a new battery fitted and still the battery is going flat we would advise checking for battery drains. This is a little more complicated, so I wont go into that!

[Pip1968]

Cheers Monkey :thumbs: I think that should do for now and I will give it a go when I get back. So in theory checking the voltage across the battery terminals whilst out of the car ie my old OEM on should be the same - 12V.

I take it that a good battery will hold its 12V if not used and out of the car pretty much continually. So in a couple of months time when I get home I can get the multimeter on it to see if I wasted my money or not.

Pip