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My Roomster is 11 months old and not had any problems until a month ago when the battery was too week to start the engine. I charged it up over night then a few days later did a couple of 125 mile trips. I didn't use it for a couple of weeks and then found the battery seemed completely dead - not even a blinking LED. RAC man came out and said battery is charging OK and thought there must too much power being drawn when parked for some reason so told me to take it to the dealer. Dealer can't find a problem and say I should use the car every week but I've often left it unused for weeks at a time with no problems before. How long should a car battery hold charge for in a parked car with alarm on?
Maybe you need a new battery?
I had a similar problem forever ago. I'd come to the car, turn the key and get "click".
Long story short, several mechanics and auto electricians later, I took it directly to Lucas who diagnosed a faulty rectifier on the alternator in about 30 seconds.
Apparently battery is OK - or so they tell me. Something must have gone bad as not as good as was.
You need to get the charging system and the battery checked properly. Check the battery with a drop tester at the very least. I have a battery and charging system analyser which tests the whole system and is very specific when it finds a fault with the battery or alternator.
Also check for current drain with a DC clamp meter. Switch the car off at the ignition key and see if any amps are flowing out of the battery. Switch the ignition on and make a note of the amps that start to be read and do the same when you start the car. Stop the engine and turn the car off and see if the amp reading drops back to zero (or thereabouts allowing for a tiny bit for any immobiliser)
RAC man did clamp test - it showed 1 or 2 amps but he thought might calm down in a while. Dealer has done something similar over night I'm told so will try to find out their figures. My guess is tracking down the cause is difficult so they would prefer to give up.
1 to 2 amps seems like a lot at rest. Should be milliamps really. Sounds like an earthing short somewhere. A good auto guy should be able to trace that.
Should be approx 40 milli amps when everything has gone to "sleep." check the radio is recording traffic announcements (TIM), also VW's (i know we're talking Skoda) when locked up the radios come on for no reason and play to themselves so keep popping back to the car to see if its come on. Also if there are faults stored in various ecu's it can keep the can bus system awake and cause a drain. Battery drains can be tricky to find but if in warranty the dealer should be finding the source.
Well Skoda dealer thought they'd fixed my problem but I've had it back a few weeks and dead again. The dealer left it connected to a machine and eventually found something that they thought was the problem and replaced it. Maybe the battery just isn't holding a charge very well.
How long should a battery last if the car's left unused?
I did not start my car for 2-3 months then it died ... so used cable to jump start later on. Initially, I could go without starting the car for 2 weeks. Now if I don't start the car for 3 to 4 days it will die.
had a similar problem with a new shape polo , aa tested the battery and found it to be fine , still not sorted the problem 😕
check it has enough water in it. I had issues with draining, the RAC man started it up and checked it and it drained straight after. Checked it myself and it was pretty dry.
Do you have an additional four way cigarette lighter port thingy for running additional stuff ie phone charger and sat nav etc? If you do and its left plugged in they will draw sufficient current over a period of non use to flatten the battery.
Short to earth in starter motor solenoid switch?
One other thing to check (as I found mine had stayed on the other day) the courtesy light behind the sun visors if they aint shut down/closed properly (or your wifes bust the little tab off the flap and not told you and shoved it loosely back in). gotta love em hey!
How long should a battery last if the car's left unused?
Battery will be rated in 'Amp/Hours. So a 50 Amp battery is capable of delivering 50 Amps for one hour. So a 1 Amp drain will flatten your battery in 50 hours - more or less. Normal consumption (with the car locked and all systems correctly shut down) will be 1 or 2 milliamps on most cars.
I suspect your problem will be a module not shutting down correctly or waking up due to a false trigger.Some cars will take up to 30 or more minutes to shut down. These faults can be very hard to catch.
I have seen the odd battery with an internal fault that would pass all the tests, but every now and then would drain overnight internally. I'd ask the dealer to fit a loan battery before I went any further, as this is the best way to rule out a faulty battery
Hth
Marko