Battery Light Lit When Idle Only

[cressws1]

Evening all,

First time I've seen this on my car. When idling the battery light comes on to indicate the battery is not being charged. The light goes off as soon as any pressure is applied to the accelerator (even when not in gear). I assume it is either the battery or the alternator, am I correct? Any advice much appreciated.

Thanks

Scott.C

[TDCiST]

id start with those yes...

Sounds like there isnt much charge in the battery, that gets boosted when revved... or the alternator cant supply enough voltage at idle, but does when its spinning faster...

Try metering across the battery when turned off, turned off with load, and same for car switched on...

Post the results back here and we can try help a bit more

[cressws1]

Sorry if this is a ridiculous question but how would I be able to do this?

[TDCiST]

if you have a friend and a multimeter quite easily!!

[cressws1]

Engine off - 12.0v

Engine running - 14.1v

What I have noticed upon inspection is what can only be described as "loads of white stuff" underneath the + terminal. Ive been out to it today and the light is no longer coming on so it appears to be intermittent. I plan to give the terminals the clean at the weekend and see if this helps. Anyone any idea what the white stuff is and how likely that is to be causing the issue? Thanks in advance.

[Stoney871]

Found on Yahoo Answers-

The white powdery substance is sulfuric acid and hydrogen crystals from the escaping hydrogen battery gases and liquid (the batteries have vents that allow the gases to escape.) This acid causes corosion of the copper wires and steel bolts attached to the battery and to some degree the battery posts and post connectors which are made of lead.

Do not get any of this stuff on you or your clothes as it is acidic and will at least bleach your clothes and if left long enough will eat a hole through them. Be sure to wash your hands thoroughly after touching the battery or any part of it.

To best clean this buildup and corrosion off, brush off the loose stuff and remove the battery terminals, then using a mix of water and baking soda together, pour over the terminals or dip them into a cup (best to use a disposable plastic cup) of the mixture (the baking soda helps neutralize the acid content and you will see a lot of fizzing while it does this, continue to use this mixture until the fizzing stops) while using a stiff brush to loosen it. You should also use a wire brush to clean the off all of the metal parts thoroughly and use the baking soda/water mix one more time (make a fresh batch). You can also use a special wire cleaning tool for the battery posts and connectors that works well to clean them to assure a good connection. You should also clean the battery off with a power washer every so often to remove the dirt and acid from the top to maintain a longer battery life, do not use the baking soda on the battery itself as it can find its way inside and somewhat neutralize the acid inside.

You can also buy special battery post felt pads at your local auto parts store that help prevent this corrosive buildup. You can also get special sprays that coat the metal parts in a coating that protects them from corrosion and dries to prevent dirt buildup. You can use grease or vaseline to coat these parts, but those attrack a lot of dirt and make for a very messy and nasty connector later on when you want to work on it again to replace the battery or use jumper cables and is very hard to clean off.

[TDCiST]

Engine off - 12.0v

Engine running - 14.1v

That's good, however repeat the same tests with some load.... Turn lights on, heated screen etc, they will drop, but if they drop stupidly fast or very low quickly means the battery has had it.. If battery is ok, and then u repeat the test with engine on but the charge voltage isn't much then alternator could be dying

[artscot79]

12.0v indicates a faulty cell in the battery any garage will check it free it should be 12.4-12.v and 14.4-14.5v

[cressws1]

Well after breaking down on the M1 at rush hour this morning, somehow getting back to Nottingham from Sheffield via the AA man borrowing me a battery for the duration of the journey, it turned out to indeed be a knackered battery. Not bad considering I've had the car 6 years and that was the battery that was on it when I got it!

£50 for a new battery fitted, bloke even cleaned all the connectors etc and put some stuff on the terminals to keep them clean, all sorted.

Thanks for all the tips and help, will come in handy in the future I am sure!

[cressws1]

Well after a week of running fine with a new battery the problem has returned today. I am now looking at replacing the alternator probably getting a second hand one from e-bay and trying to fit it myself as a new one is looking at costing me £150 approx.

My question is do the 1.8 petrol and the 2.0 petrol use the same alternator? I have found one on eBay in almost new nick but its advertised as a 2.0 engine one...

Any help with this greatly appreciated.