Update: multimeter readings!

Leave the car overnight, then test the voltage before starting it.

If it's more than about 12.5V, it's fine.

Chris

He's full of s*it.

I just paid £42 for a Bosch battery, 3yr guarantee, with enough capacity for a diesel transit van.

Conor ( snipped-for-privacy@gmail.com) gurgled happily, sounding much like they were saying :

Looks fine though as someone else said test it after leaving it over night.

Take it with a pinch of salt.

Voltage readings mean very little except as a very rough guide to the state of charge. He should have had a proper battery tester that puts a very high but brief load on the battery and analyses the results.

What Dave said about testing under load. I recently bought a Bosch battery for my Golf (MK2, 1.8, I'd guess it's harder work to start that most Polos out there) - £30 ish from GSF, about £3 more than a yumcha brand, and about

With the greatest of respect, I beg to differ on three counts.

If a battery has one weak cell, but is otherwise sound it may continue to start the car for some considerable time. If you are running an old car into the ground, that might be all you want. Using a high-discharge tester on such a battery will usually kill it stone dead.

Testing battery voltages, if done appropriately and analysed sensibly, will often tell all you need to know. In addition, you will learn if the charging circuit regulation has failed in a way that causes the battery to be over-charged. No amount of discharge testing can do that.

Finally, if you want more than a rough guide to the state of charge, you need to use a hydrometer and thermometer - not always possible on modern batteries of course.

Chris

Two things. The old fashioned high discharge tester takes no more current than can the starter, so if it kills the battery, so will the starter. Modern ones (which my local Halfords use) look rather similar to a multimeter and put a short duration high load on the battery under microprocessor control and analyse the results. They can therefore give a readout of the battery parameters without the need for human interpretation - no bad thing when you're talking some Halfords 'technicians' as the OP's anecdote amply demonstrates.

Sensibly being the operative word. But this requires knowledge. For a start, there's no point in testing the off load voltage immediately on a battery that's been on charge - it must be left to 'settle' for several hours.

Indeed - however that wasn't the point I was answering. The Halfords bloke was talking about battery voltage.

All you need these days is a decent battery tester. They're not cheap, though. But you should find them in any decent place that sells batteries. Finding an operative that doesn't lie about the readings might be more difficult.

My battery is crying for a change, been meaning to get round to changing it. I've always seen bosch as a good brand where did you find the £42 one from ?

Local motor factor.

Never trust a car parts salesman.

What are the symptoms for all this mucking around that you are doing?

e.g. watch the reading whilst somebody starts the engine. 12.4V is fine, but tells you nothing about the batterys ability to start the car.

My car was a little sluggish when starting in the mornings so thought I'd see if it was a battery \ alternator problem. And its a new skill I've learned thans to the folks in here which I owe them a drink for :)