navigator

i know this is an electrical section question but i think it could be of wider interest given winter is coming to all users:
My battery has just failed, and the car wouldnt start as a result...lights,radio alram all still worked though.(battery was knackered when it was tested)

Question when you start your scoob what do you have to do before the alternator puts the battery back to where it was before you started?
A) do you have to rev above x revs before alternator puts any charge in charge back?
b) have to run the engine at x revs and for 5 mins say
c) just drive round for 5 minutes with lights radio air con turned off.
d)how much juice does the alarm take out in additon

So i guess what i am looking for is a simple rule to answer the question
e.g. Start the car,leave it on tickover with radio,air con,lights switched off for 5 mins and battery is re charged back to where it was.

hope there is a techie out there who can offer advice.

easyrider

The alternator should put charge back into the battery even on idle even with lights on,its questionable as to how much if youve got all youre ancillerys on though.
They say that it takes about 14 miles of driving to put the charge that you use starting the car back into the battery-dont know worked that one out though.

easy

grabber

had the same problem m8, only advice i was given is to use a battery charger/conditioner on a regular basis,

Welloilbeefhooked

iTrader: (3)

To recharge the battery after starting will depend on what other electrical equipment is being used at the time as you quite rightly pointed out.

From what Lucas have always said, they recommend 20 mins of driving, assuming the alternator is working ok, to recharge it to its previous state. This is with no other elctrical equipment in use.

navigator

thanks guys. helpful replies as ever.
14 miles or 20 mins..... its a good deal longer than i thought.(with every thing off).
so 5 miles to work with radio and air con and wipers (well it is summer) on...no wonder i flattened it.
I wonder if investing in a battery charge is a good long term deal rather than £60 + for a battery even with 4 yrs warranty.
food for thought and a trip to hell fords maybe the wek end.

easyrider

Chances are its probably just a duff battery-as you should be able to go for a few years without recharging-if you have the same probs with the new battery,then is probably the alternator starting to go.

easy

navigator

thanks for that m8. useful information.

THE M25 FLYER

RAC recomend that if we attend a discharged battery (lights left on etc) that after jump starting the vehicle should be driven for about 45 mins with all loads off to recharge the battery to about 80% Its claimed it can take 450 miles of vehicle use to 100% fully recharge the battery,but 80% is fine.

ShyTot

See www.accumate.co.uk
for just about the best battery charger / conditioner you can buy.
The standard Accumate is fine and it comes with a fused link for quick connection to the battery.

I use one all the time.

ChungsterSTI

Having Flat Battery probs too on my own 03 STI.

With a Multi Meter....engine idling the alternator is showing a charge of 12.5v. This apparently according to a dealer is how it works. It does not throw the full 14v into the battery unless the battery has more load on it.

So I switched the side lights on. Alternator went upto 13.5.

Switching driving lights on and air con and other bits....alternator went into full 14v charge mode.

Bit weird cos that means if you're not driving round with lights on then battery never gets charged up properly I guess.

With engine off my battery is only showing 12.5v. This is a dealer replacement job that has already failed once since install (left it for 48 hours!!) Previously it died after leaving alone for 7 days.

easyrider

Sounds more like an electrical fault which is drawing power from your battery when left off-a faulty immobiliser/alarm is a fairly common fault-best to let your dealer trace it.