Battery

Sometimes they just die on you. But it's always good to regularly check the electrolyte levels and keep them topped up with distilled water. Batteries branded as "maintenance free" are misleading, as any battery ideally needs the electrolyte checking! The original battery on my Renault Master gave up after just over 6 years, which is a reasonable enough life for a battery these days, but looking inside it was completely dry - if it had been checked and topped up all its life it could well have lasted 10 years or so. I blame the parents.

Peter

-- "The truth is working in television is not very glamorous at all. I just go home on my own at night and sit alone and eat crisps."

They can fail without warning, and are not usually checked at a service.

The message from "SimonJ" contains these words:

What is? (that was asked in the spirit of sarcasm - please don't supply a list!)

The message from "SimonJ" contains these words:

It's not unknown for garages to tick all the boxes on a checklist without having actually done some - or even many - of 'em.

A check it with hydrometer, and a heavy discharge meter, gives a very good guide of it's condition. Even SG's, with a good steady discharge reading means the battery is probably good for another few months.

Nope. If you're lucky they might top it up. But nothing more unless it fails during the service.:-) Mike

If the battery is good but just low on charge, the current will be higher at first, and decrease as the battery nears full charge.

However, if the battery is faulty or has been allowed to go totally flat and the plates become sulphated, its internal resistance will be high so it might draw very little current.

If you have a volt meter (DVM etc), check the voltage with the charger on and off. It will be higher when on if it's working. I'd expect to see about 14 volts.

If the voltage is ok and the battery is sulphated, sometimes leaving it on charge for several days might partially reverse the process - but this isn't guaranteed.

Ideally the other way around I'd guess. The needle's indicating the charge rate which I'd expect to (roughly) go from high to low.

Assuming the battery is not dead flat (which may stop the current getting through, initially) the needle will go right up and as the battery charges (effectively producing a steadily increasing 'reverse' current) the needle will go back down. The needle is indicating the amount of current that is going through the battery to charge it, not how much charge there is in the battery.

Rob Graham

OK guys thanks. We've come to the decision that the charger is screwed. (it's seriously old.)

Check it doesnt have a screw in fuse somewhere - unregulated chargers often do and they can blow.

it's in the garage and I cba. Saturday he's off to buy a new charger and seewhat that does. I just *know* there's something in the car draining the battery when the engine is off, so whether he gets one or I do, a voltmeter thingy will also be purchased and the battery output checked when engine is off. Then if the output is higher than it should be (0.05A iirc) he can remove the fuses one by one to see what's causing the drain and try to fix it. He's the car expert, I'm the one who has that ever dangerous 'little knowledge' from reading usenet groups and forums :-D

There will be. You can expect something like a 40 milliamp drain. To check this, remove a battery lead and connect an ammeter btween the battery and the end of the lead. If it's a lot higher then you may have a problem.

Rob

If it's a modern(ish) car with central locking it'll try to relock all the doors and seriously upset the ammeter. You ideally will want a clamp on type.

What battery voltage would you consider normal on a frost covered car that's been stood outside in the cold overnight with temp around -4C?

The message from "Mark" contains these words:

The same as usual off load. The electrochemical potential between the two plates doesn't vary significantly with temperature.

Of course, the /on load/ voltage will vary far more with a cold battery as the chemistry all works slower so the internal resistance is higher.

you mean one I can just clamp on in situ without the car chucking a wobbly and locking doors/setting off alarms?

Yup.

right-oh thanks. Always wise to answer me in moron, I'm fluent in moron. ;-)