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Battery on my Passat has seemingly flattened overnight, any thoughts on likely causes? It's a daily runner, had been used yesterday then when the Mrs went to start it this morning it was flat. It's a 2007 Passat, probably on the original battery at a guess. Cold weather finished it off maybe?
I think you've got it with the cold. Older batteries don't like the cold and being dead on a cold morning is often the first time you realise it's on its way out.
On a positive note 9 years is pretty good going for a car battery :).
Short journeys with everything switched on? Or could just be the cold
You say it's a daily runner but what sort of distance do you do in it daily? and what sort of engine (petrol/diesel)?
Using heaters, lights (does it have auto switch-on lights?) fans, aircon, etc, can all drain the battery and if it's only being used for short journeys it's likely that in colder weather it's not getting a decent charge back into the battery from the alternator to counteract all the drain put on it.
Add this to an old battery it may be that it just can't cope wit hthe extra work this weather is putting on it but it's also possible that it may just need a proper full charge.
It's mixed use, Mrs uses it most days to commute/pick kids up (15-20 miles a day) & I use it for longer journeys once or twice a month. She wouldn't know how to turn half the gizmos on TBH, doubt she'd ever use the heated screen or mirrors!
Passat 2.0Tdi
Kid playing with interior lights and one been left on?
That's what happens to ours regularly (well used to until we started treble-checking).
old, cold battery is a reasonable guess.
especially in a diesel car, when the first thing you're asking it to do is provide a large current for the glow plugs.
At that age you might as well a new battery anyway, but also no harm in checking that it's getting well charged (ie voltage when the engine's idling). I had flat battery issues a couple of years back, put a new one in and it worked ok until the alternator died within a few months (by which time it had partly damaged the battery again).
Since getting a new alternator it's been fine until a couple of days ago when it was flat again, which I put down to a lot of stop/start trips (inc MOT test) and the cold weather on top of the battery being a bit knackered anyway.
Interior light is a maybe, though I thought they went off when you locked the doors. I may be wrong!
Just a bit surprised that it could suddenly (apparently suddenly anyway) drain when it had been absolutely fine, never had any issues starting the car. And it was actually warmer this morning than it has been over the weekend (and it's been fine), no ice on windows or anything.
Check the terminals are still attached and not corroded.
Drove my wifes Ford Ka to the petrol station and getting back in,nothing.
Battery dead.Got the AA out and battery was finished. I said it had started with no problem but the AA guy said batteries nowadays tend to just suddenly fail.
Just a bit surprised that it could suddenly (apparently suddenly anyway) drain when it had been absolutely fine, never had any issues starting the car. And it was actually warmer this morning than it has been over the weekend (and it's been fine), no ice on windows or anything.
pretty much every battery I've had fail has done this. fine one day, as good as dead the next.
interior light left on is one usually touted by one clutching at the last straws.....hell ive left the (led)side lights on in my landy over the weekend and its still started on monday morning.
I will go with cold how ever i wouldnt declare it dead till id measured the outgoing voltage....
a poor/corroded earth strap and a whole host of other causes can masquarade as a dead battery
Interior light is a maybe, though I thought they went off when you locked the doors. I may be wrong!
No - they have three settings - off, auto (goes off when door closed and sometimes on lock depending on the feature of a particular car) and always on.
interior light left on is one usually touted by one clutching at the last straws
I disagree - our Mazda 3 will get a flat battery if the interior lights are left on overnight - did it about three times when our girls were a bit younger then the battery failed terminally.
nasty. my peugeots even on always on - will go off after 5 minutes.
sounds like a poor design - thatll be a first for a peugeot to beat the east when it comes to car electric design.
There's a relatively straightforward set of tests you can do with a multimeter to diagnose this. Sometimes you might not even need that (both my Focus and Astra have had hidden diagnostic menus capable of measuring the voltage).
http://www.wikihow.com/Check-an-Alternator
I'm pretty sure most modern cars fast-charge the battery in the first 10 minutes or so, making it unlikely a series of short journeys will drain the battery unless somethings wrong.
I'll give it a once over later, make sure everything's looking ok under the bonnet. Though it's 2007 it's low miles so maybe the battery has had a hard life of short journeys prior to my ownership.
Classic battery dies during first sustained cold weather imo and as you suspect