Car Battery, why will it not start the car?

  Sapins 08:15 25 Jul 2010
Locked

A few days ago I tried to start the car after it had stood overnight, and it appeared the battery was completely flat, I know, I know, What shape should it be! anyway I jump started it from another car, started first time so I visited my local dealer who tested the charging rate and found that adequate, but he did say something could be drawing current when it was just standing, I had double checked the there was nothing left switched on, so he advised me to disconnect the positive lead, the same thing happened the following morning and when I tried everything electric, lights, wipers, radio etc; they all worked perfectly, still would not even turn the engine over so back to garage who could not fit me in till next week but in the meantime they replaced the battery and the car started immediately the next morning, so, if the battery was showing a full 12 volt charge, which it was and the charging rate was 14 volts+ why would the car not start?

  BT 08:25 25 Jul 2010

I had a similar problem with my Fiat Stilo earlier in the year. One day the car would start and next morning it wouldn't. Similarly with battery which was almost new. Took it back to dealer who tested it and said it was OK. Never did find out the real cause. My nephew who is a motor mechanic had a good look at it and the only thing he could find was corroded terminals on the starter motor. He cleaned up one of them but couldn't undo the nut on the other one, so it never got done. Bad positioning on the starter motor just under the front of the engine with no covering and gets all the muck thrown up on it. Bought one of those emergency engine starter battery packs. Don't have the car now.

  zzzz999 08:54 25 Jul 2010

If the battery is ok and the mechanics (engine, starter motor and alternator) are fine then its a connector problem. Sometimes its just worth replacing the leads every few years to solve any cracks causing problems. I also give the connection points a squirt of WD40 during the winter months.

  wiz-king 09:04 25 Jul 2010

It is not the Volts you need to start a car but the Amps, about 200 - 400 of them. As lead acid cells age they will still hold a charge and give 12v off load but the amperage goes down when you put a load on. Most thing on a car will only take a few amps at most:- radio 1amp, even the headlights only take about 15amps the starter is the biggest load by far, if you have a diesel the load is higher because of the higher compression of the engine and it may also have heaters in the fuel injectors.
Poor batteries! The have got smaller but have to work harder with all the gadgets on modern cars - heated seats, electric locks etc.

  Quickbeam 09:15 25 Jul 2010

wiz-king's right, I've had batteries in the past that have past the condition checks, but won't hold a starting load.

Batteries do wear out, and any starting problems are best dealt with by putting a new battery on if it's a few years old, even if you then trace the problem to another fault it's not money wasted, but 9 times out of 10, it'll solve the problem.

  morddwyd 09:33 25 Jul 2010

Batteries have come on quite a lot, but they still suffer from vibration, engine heat and regular extremes of temperature.

It used to be rare for a battery to last more than two winters.

They should always be tested under load, ideally one cell at a time.

I used to have an old Rover (P4) where there battery was in the boot.

A long supply lead, but no vibration and a relatively stable temperature kept it going for five years or more.

  dagbladet 09:37 25 Jul 2010

"They should always be tested under load, ideally one cell at a time."

How?

  Fruit Bat /\0/\ 10:43 25 Jul 2010

Any garage will do a battery (voltage) "drop test" for you.

click here

  Quickbeam 10:47 25 Jul 2010

But be warned, if your battery is is near the end, the drop test can kill it instantly, and it will not hold a charge any more:(

  Fruit Bat /\0/\ 10:50 25 Jul 2010

"It used to be rare for a battery to last more than two winters."

Yes first sign of cold weather used to catch many people out as battery started to fail.

A friend of mine had a battery freeze up on him, in France this winter.

My 13 year old Micra still had the original battery when I swapped the car last year.
Modern batteries do not need constant topping up of electrolyte (sealed for life), just keep charged and keep terminals cleaned and greased is all the maintenance required.

  jack 10:50 25 Jul 2010

They should always be tested under load, ideally one cell at a time."

How?
Quite right with modern designs covering all terminals.

Many things with the start sequence go wrong
and because of the high demand at start cause a failure.
Some vehicles have the exhaust manifold over the starter- Heat degradation of the main current and the solenoid cables will cause high resistance.
The push on spade connector to solenoid can become corroded.
This caused me much trouble with a Renault 11 to wards the end of its life.

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