New car battery gone flat...

Eddzz!!

Eddzz!!

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Eddy
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Any petrol heads around here shed some light on why this has happened? Before Christmas I replaced my car battery with a new one (after the old one kept going flat). Now the main thing I can think of is that I don't drive the car enough. I live in a small town and the most that the car gets driven is a couple of miles a day, if that. Will this not be enough for the alternator to charge the battery? The car battery died after I left it for a week while I was away on holiday. I've come back to it not being able to start, though there is enough residual power remaining to operate the ignition, central locking and in-car electronics.

Any ideas? I swear to God, cars are more hassle than they're worth! :confused:
 
Sounds like something is still drawing current, auto electrician time I fear!
 
as already suggested, duff alternator or a current drain.
two mls a day is not a lot but it is enough to stop the battery going flat providing it starts on first turn.

Inside light left on?, boot light, under bonnet light, radio/ cd player, badly fitted/poor quality alarm, under body light kit. LOL
 
It always used to take an alternator about 15-20 minutes to recharge the battery by the normal energy consumed during the engine start, probably a bit less now, so if all you do is short journeys and don't rev the engine high (charging rate is proportional to revs) then it could be usage pattern. Also cars nowadays have alarm systems and the radio consumes a trickle of current when not in use.

You can get solar panel chargers which plug into cigar lighter socket to trickle charge whilst car is parked, but unplug before starting.
 
A few miles drive isn't going to recharge a battery. It will continue to go flat. It also kills batteries to have them flattened like that.

Your only solution is to take the car on a proper run once a week. Minimum 45 minutes. Constant short piddly journeys won't do any petrol/diesel car any good. Only sort that would be any good are the plug in electric only ones as they don't mind.
 
How old is the car? If it's fairly recent it may have a smart charge alternator which only charges the battery when you are braking, slowing down. If you're not doing much of that during the 2 miles to and from work, the battery won't be getting a good charge. Also was the replacement battery the same rating as the previous. If it was a much lower rating you'll be using up all the charge and with such a short journey, not recharging it enough.
 
Never had that short journey problem with mine, you have a fault and it's time to pay someone who knows what they are talking about to fix it :whistle:
 
I had a similar-ish problem recently - battery not going flat but certainly losing a lot of its charge due to lots of short journey use. There was no current drain or poor alternator, just a combination of an oldish battery and short journeys in the cold.

For £50 I bought one of these trickle chargers. Due to its connector system, it's really simple to use and you can charge the battery in-situ - it's made a fantastic difference. The only caveat is that you obviously need to get your car close to a power supply but if you can it's certainly worth considering.
 
Had the same problem, it turned out to be the radio which was drawing curent even though it was 'off', I only discovered that when I changed the radio and the battery problem went away.
 
Nowadays it takes a very short of time to recharge the battery after starting as engine management (on petrol and newer diesel cars) means cars generally fire within a few seconds rather than potentially needing a lot of cranking like in the good old days of points and condenser ignition and carburetors. Two miles of normal driving will typically be enough to recharge the electrical power expended in cranking the starter motor, unless you are using every electrical device attached to your battery during the journey - while it isn't MOTed at the moment, I have an ammeter attached to my Imp so can see when the charge drops to 0amps after starting and it is generally under a minute. A couple of miles made up of four separate journeys is another matter though.


Check the following:

1) Alternator belt tension (n.b. there may be other things driven from the same belt, e.g. water pump, power steering, aircon, etc. but not generally the camshafts. Or the fan. Been a long time since cars had "fan belts")
2) Voltage across the battery with the engine running (should be 14V or more, if it's not the battery won't be getting all the charge it should and it's indicative of possible alternator failure)

After that you're into checking the current draw with the ignition off to see if you've got something draining the battery all the time, for example an interior light that never goes off.
 
Good to know. I suppose with lots of cars having stop/start too charging rates would have to be better.
 
AHILL said:
Inside light left on?, boot light, under bonnet light, radio/ cd player, badly fitted/poor quality alarm, under body light kit. LOL
Click to expand...

My father had the mysterious flat battery syndrome, it was found to be a dodgy boot light switch. It was only found when he noticed light shining through the rear seat gaps one night :D
 
Check the alternator is charging the battery properly but I don't think you're doing enough miles. Starter motors use a lot of power. Also has it got an alarm? If I don't keep my bike plugged into a trickle charger the alarm flattens the battery, and will kill it if left too long.

However, my bike isn't used for weeks sometimes but if your battery isn't getting the charge due to low miles and then you leave it for a week it won't help.

One other thing battery aside if you only do a couple miles a day you are going to kill your car because its just never warming up enough. My advice, cycle or it'll be more than a battery going wrong.
 
andrewc said:
You can get solar panel chargers which plug into cigar lighter socket to trickle charge whilst car is parked, but unplug before starting.
Click to expand...
That's pretty damned cool!
I didn't know that.
 
There are a lot of sensible good suggestions here and all possible explanations.

However, if you really are only driving two miles a day, that's not very far at all. Asother people have said, it's quite feasible that there's nothing wrong with the car but it's just not enough use to keep your battery charged! Especially given your point that the old battery kept going flat while this new one has kept some level of charge for four months since Christmas ... and that was through all the winter wind and rain and demister fan and HRW and wipers and all the other electrical drains.

What sort of car is it and how old?
 
Solar powered chargers work best when you start off with a fully charged battery. I used to have one. Also check that the cigarette lighter socket is live when ignition is off and that it does pass charge through as not all do. I had one years ago.
 
My missus does the same sort of journey in her yaris a couple of miles every day
She's never had any starting problems but i do try to take it for a good run at least every two weeks as short runs dont do the engine any good
The voltage test across the battery is a great idea and is easy to do
 
lot of internet answers here too.
you have something using the battery when the car is parked.
knock engine off and start at your fuse board and a fluke. See if anything is drawing power.
check the obvious
radio
alarm
immobilizer.
trickle charger is a good ideal. If cigarrette lighter not directly connected then run it directly of the battery terminal.
look to maplin £12 for a solar powered charger.
im too lazy to message more
ps im an electrical engineer
 
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A few years ago, we got rid of a Mazda 3 - supposedly a great car. It had numerous faults despite being in warranty, including the original (less than 3 year old) battery going flat. The dealership adopted the "ostrich" pose, so we got rid.
I run a 14 year old Mondeo as our second car, and it is on its original battery.
I should mention that the Mazda was getting a regular 50 miles per day motorway runs, and the Mondeo does all the short runs, as well as being left standing for days/weeks at a time.
Like many consumables, I suspect that batteries are designed to fail after a very short period of time.
 
andrewc said:
It always used to take an alternator about 15-20 minutes to recharge the battery by the normal energy consumed during the engine start, probably a bit less now, so if all you do is short journeys and don't rev the engine high (charging rate is proportional to revs) then it could be usage pattern. Also cars nowadays have alarm systems and the radio consumes a trickle of current when not in use.

You can get solar panel chargers which plug into cigar lighter socket to trickle charge whilst car is parked, but unplug before starting.
Click to expand...

Charging rate is not proportional to revs - common myth - if it was the accessories and lights would get brighter (or burst) when you tanned it and would go dim when you were idling. An alternator in good condition puts out around 14Volts no matter what the engine is doing.

If the OP has an alternator problem the battery light should be lit on the dashboard while the car is running to show it is not charging. If the belt is loose and not turning it, this will be easy to tell by looking in the engine bay (and listening). If there's an electrical component drawing power, this is also quite easy to isolate if it's an older vehicle by pulling the fuse for certain systems one by one. I suspect something somewhere is stuck on though. Things like vanity mirror lights, boot light, glovebox light. They don't use much in the grand scheme of things but if stuck on and the car sits a lot it'll soon sap the power out of the battery.
 
How would one go about determining what exactly is draining my battery if it is indeed an electrical component? Pull a fuse a day and see if the car battery continues to go flat? it started fine this morning after I drove it around for an hour last night! I drove for another 30 minutes this morning and now the car will be sat outside the office all day until 5pm.
 
Well, yes. The sparky above me said it and I agree. You're only going to find out what's draining the power by process of elimination.
 
Yes, charging voltage is maintained at around the 13.5 to 14.5 volts, but the charging current varies. At idle it may be charging at around 10 amps, whereas under full load at high RPM it may be giving maybe 70 amps or more, but the charge voltage is still at 14 volts or so.

If you want I can provide a graph from an alternator manufacturer showing the charge current increasing with revs. Due to the gearing effect of differing pulley sizes, an engine may run between 0 - 7000rpm, but the alternator may run at up to 15,000 rpm.
 
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