[Closed] Car battery flat after a week?

It will take quite a while to regain lost starting energy, so lots of short journeys in cold weather may never replenish the battery. I had this with my Golf last winter, I was driving it regularly but never for long enough. I now use a smart charger on it for six to eight hours every two or three weeks if I am not using it much.
Leaving it running in the street unattended isn’t great for emissions and will invalidate your insurance and could lead to a fine.
How you drive it doesn’t make a lot of difference to the charging as far as I am aware, it’s time that will do it.

Probably best to get it connected to a charger and get a full charge into it. You're talking a day to do so fully. It's not normal, but if you're only doing short journeys it could have been running low for a while. Charge it for 30 mins or an hour and it will just happen again.

USB thingy in the fag lighter?

I'm no expert but a mate was told this had been the cause of his wife's flat battery a couple of years ago, lad a couple of doors down had the same

Right, thanks. Any recommendations for chargers?

Any decent make charger would do, Autoexpress test them every year and the Ctek ones usually come out best but are expensive. I have a Sealey one that was last years runner up on their tests- not the one in this review below though
https://www.autoexpress.co.uk/product-group-tests/351865/best-battery-chargers

Twenty-year old car emptying a new-ish battery in a week, I'd be looking for water ingress. Starting with the rectifier pack on the alternator.

Also consider, if it's been deep-discharged it might well be donald ducked now even if it wasn't previously.

Twenty-year old car emptying a new-ish battery in a week, I’d be looking for water ingress.

True if it was fully charged at the start, but if, as with my golf it had clearly been slowly losing charge and not replenished and after a layoff wouldn’t turn over, you might be lucky like I was- the battery is fine 18 months later.

Twenty-year old car emptying a new-ish battery in a week, I’d be looking for water ingress. Starting with the rectifier pack on the alternator.

Water ingress is an ongoing issue. It goes mental in heavy rain and has left me stranded before. Also, if I wash it the speedo resets.

I thought I'd cracked it earlier in the year when I found loads of old leaves blocking the drain scuttle, cleared it all out but maybe it's still getting in somewhere ;(

I used to have one of those solar powered trickle chargers on the dashboard of my old Capri, then a Manta, then an E30, then a 740. On an old car that was driven once a week max it made all the difference between firing up convincingly or taking a bit of persuasion.

I think they're still about 20 quid and you can just leave it attached while you drive around. It won't charge a dead battery but it'll keep a good one topped up.

Water ingress is an Ongoing issue

what model of car is it?

Is that normal?

Yes, in many circumstances. As above - they do discharge on their own, slowly, and the car's alarm does drain it a bit. And yes without long trips it won't get fully charged.

A lot of people say 'oh plug a solar panel into the 12v socket' but tbh I don't think I've ever had a car since the 90s where the 12v socket was live when the ignition was off. You can apparently plug them into the OBD socket, which I have to look into.

Do you have a volt meter?
Check battery with engine off..
Check battery with engine running..
Will tell you if the alternator is charging the battery

I wouldn't say it's normal at all. We often don't drive for weeks and it's fine. Some cars are worse than others but a week is way too short. If it's been doing it for a while but masked by you driving regularly then it'll hurt the battery. Lots of possible causes. I had a car with a dodgy door switch. It'd turn the interior light off but it would come back on at some point.

As above check with a meter that it is charging. You can also put the meter in series and measure the discharge current

As Cloudnine says, need to check voltages. Could even be the battery and not an electrical/alternator fault.

Thanks everyone. It’s an old VW Polo. Starter replaced last year. Alternator and battery two years back.

The jump-starter still charging so will leave it till tomorrow. I do have a volt meter but can’t find it anywhere, possibly lent it out… will go and buy another tomorrow.

One week is rubbish, I sometimes only drive once a week and though I've had a flat battery a few times there's been some other underlying fault each time (alternator problem or lights left on, most recently a faulty switch).

Fag lighter is probably not connected when ignition is off - suggest you check this before looking further into that as the problem.

As a slight aside - to charge a car battery, is it enough to just have the engine running or does it have to be driven? My older brother told me when I was a kid, that the car has to be turning it's wheels to charge the battery! But he may have just been at it...

You need the revs up to pump out the 13.5 volts from most alts to charge
And the battery must be tested under load ie when cranking the key. Anything under 10 volts when cranking it's new battery time

Does a flat battery seem the most likely culprit btw?

I just assumed. Lights come on but dim when attempting to crank. Then a sound like the starter barely moving, then nothing.

As a slight aside – to charge a car battery, is it enough to just have the engine running or does it have to be driven?

Mercedes can be made to display the battery voltage and current when off or when driving. On mine, the battery voltage and charging current are no different at idle or at higher revs.

As a slight aside – to charge a car battery, is it enough to just have the engine running or does it have to be driven?

To get any meaningful charge in a jumped dead battery you’d have actually drive it, and for a decent amount of time, 10mins won’t be enough.

Fag lighter is probably not connected when ignition is off – suggest you check this before looking further into that as the problem.

older vw’s cigarette lighters are not switched with the ignition. I’ve got a Bluetooth/FM thingy I have to remember to unplug in the van if I’m leaving it for a bit as it drags the battery down.

I discovered the hard way in my Subaru the only thing that isn’t switched off when you lock it, is the light on the vanity mirror on the drivers side shade. Away in the states for work for 5 days and totally flat battery when I got back.

Yeah, now I think about it. I always notice a stupidly bright blue LED on the USB thing even when the car's parked. Never really thought anything of it as I usually drive it every day. But that must mean it's still draining some power.

To get any meaningful charge in a jumped dead battery you’d have actually drive it, and for a decent amount of time, 10mins won’t be enough.

Pessimist!

Leave it till a nice Sunday morning, jump it then park it up in neutral on the drive way and put a brick on the gas pedal to keep it bouncing off the rev limiter.😁

Guaranteed to get admiring glances off all the neighbours.

My 2009 polo does the same thing. Never found an obvious cause. Happens with new and old batteries. Has been the same for years. In winter if left for three or four days I need the booster pack to start it.

Could be any number of things, easier just to manage it.

My Fabia (basically a Polo) used to regularly sit for a week at a time with no issues whatsoever so you might want to look at any current drains. It could also be poor earthing of the engine though as corrosion could be an issue. That was the root cause on an old Corsa I had that killed a new battery in a few weeks, it wasn't able to run the car and sufficiently charge the battery even on long runs.

Yeah, now I think about it. I always notice a stupidly bright blue LED on the USB thing even when the car’s parked. Never really thought anything of it as I usually drive it every day. But that must mean it’s still draining some power.

I've got a USB adaptor permanently plugged in the 12v socket by the handbrake that's always live, powers a BlueTooth adaptor for the stereo. The actual unit switches off after 5 mins but the adaptor always has it's blue light on, never had an issue. I've also got a dashcam that's permanently powered too. The car is 9 years old and still on it's original battery and alternator after 135k too. I was worried about the battery for this winter and nearly changed it as a precaution but haven't yet, might do that soon though.

It’s not really normal.

I regularly leave mine for a fortnight (longer at times) and it always starts with zero issues. It’s the original battery on a 10 year old car.

It could be something draining it, like your Blue LED or aftermarket radios are a favourite in VWs.

Could be a dead battery or alternator too.

Or any of the other suggestions above.

My old T4 had a broken wire on one of the relay feeds, the “fix” was to put a jumper wire across the relay terminals which was great except it would slowly drain the battery after 4 or 5 days if I forgot to pull it out.

Mine does this although it seems fortnightly seems to be the point, went through a battery every year, I now 7-10 days run it down the motorway for about an hour just to tick it over, I don’t drive for work and feel the car could go but insurance pricing etc it’s cheaper to keep the car.

Off to do the battery run today!

A CTEK battery charger / reconditioner is what you need.
We have a 1992 Merc, a 2007 Alfa and a more modern Jag in the house and the CTEK is used once or twice a year to recondition their batteries.
Plug in and leave, it takes 5-6 hours and is brilliant. I know others use them hooked-up on Trickle charge mode

See https://www.ctek.com/uk/battery-chargers-12v-24v/car-charger

Widely available (even Halfords).