(G) Battery Madness

So, for the last 3 days, and after 1200 miles of trouble free motoring (excluding a frozen blue and me that was fixed with battery disconnection for 2 secs), my car decides to drop the fuel display from half a tank to 0 instantaniously, as well as the fuel warning light coming on! Got worse to the point of doing it every minute or so when i was driving yesterday. Took it into my local Fiat dealer who would let me know at lunch time what they found, which was basically that my battery was showing lower charge than it should, and this was causing quirks like the fuel guage freaking out! They're keeping it overnight to charge back to where it should be.
My argument is - why do i have a battery that isn't holding charge on a car just over a month old? They say that if you do short journeys frequently the battery doesn't get a chance to charge again - isn't the 500 supposed to be a city car? This sounds stupid and implies that it could happen again at any time unless you drive for longer journeys!!! It didn't apply anyway to me, so the next one was that it may have lost charge before it arrived at the dealer - why wait for 6 weeks to play up then?
I would feel much better with a new battery, then see if the car was causing it to lose charge - am i being unreasonable?

Hi Mate.......
Was your battery reconnected nice and securely after disconnecting to reset blue and me? Maybe you were not getting full charge due to a loose terminal.

Modern batteries in my experience regain charge VERY quickly even when only doing short trips around town. And I assume your car had enough battery power to start the engine?
Sounds like an odd diagnosis from the dealer re your fuel gauge problem!

With a new battery stop start shouldnt affect it that much, and the charging system in your 500, being a new car should be more than capable of coping with it.

Could be a problem to keep an eye on. TBH even a loose battery connection shouldn't cause it as the charging system should still supply enough charge even if the battery were removed compleatly.

Jon.

Modern car alternators only produce a charge when needed due to the back emf.

Cheers

D

emf

And how does that system work out of interest? I assumed that because its always turning with the engine, its always charging.

Jon.

After about 300 miles, my battery somehow discharged itself while the car was unused for a couple of days, and the engine would not start. When the voltage is that low, I can tell you that the whole electronic system goes bananas - not just the fuel gauge, but I had all sorts of dire warnings about everything flashing up. I charged the battery for a couple of hours, and everything has been fine since. But I still don't know what caused the problem.

John

You'll probably find that there is some sort of clutch which allows the alternator to disengage meaning there's less drag on the engine.

Cool, still seems a bit pointless though, lol.

Not really. Think of driving all the time in a car with air conditioning on when it doesn't need to be on. Saps power and uses fuel.

True, but air con compressor is a hefty thing to power, but aultinator isn't that hafty is it? I know what your saying though.

Cheers for all of your replies.
Picked her up at lunchtime and all they'd done was re-charge the battery. Not totally confident 'cos why did it discharge in the first place? Hate to thik what would have happened if I'd used aircon, heated rear screen etc.!!!
Nothing i can do about it other than drive it for a week then take it back in for them to see if it's down on charge. Hmmmmmm.

EMF = Elecromotive Force.

Basically what Rallycinq is getting at is that there is a control unit in the Alternator that regulates the amount of charge it produces dependant on the load. It does this by outputting a constant voltage (usually around 13.2 to 14.2 volts)to the whole of the electrical system and across the battery which, as well as storing charge acts as a capacitor to smooth out and electrical 'spikes'. If the battery state is healthy the alternator wont need to be providing much current to maintain this voltage (trickle level)

For a discharged battery and/or heavy use of electrics/ lights/ sound system the alternator will be providing more current to maintain the correct regulated voltage. Ohms Law!

it also prevents the alternator from boiling the battery best thing you can probably do especially on a new car if it wasn't done on the PDI is clean the battery terminals with a bit of sand paper and apply a smear of grease or Vasaline to the terminals and battery clamps..

which is exactly what happened to my mates TVR

then the battery melted it's way down through a few panels



I didn't laugh . . .much . .

Ouch!