My 2005 Forester's battery drains slowly over several weeks. I put a slow charger on it to recharge, but it continues to slowly drain its charge. I read that the car has certain electrical functions with its computer that continue working even while not running. However my 2010 Forester doesn't have this same problem, so I suspect there is some short somewhere in the system that is causing a greater drain on the battery's charge. Any suggestions on how to diagnose this issue or how to locate a short?
Slow draining battery on Subaru Forester 2005
- Thread starter BillG
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do you have a meter? youre doing to need one. see how much its drawing when not running, then start pulling fuses until you get the one that's causing it. from there youll have to physically trace out the problem circuit. these are always my least favourite type of problems, good luck
although i am curious, is it only going dead only after sitting or is it also dying when youre out and about using it?
although i am curious, is it only going dead only after sitting or is it also dying when youre out and about using it?
Thanks, that's exactly what I've been doing.
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What he said.
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he does say in the post it still goes dead despite trickle charging
No, possibly I wasn'y clear enough. It doesn't go dead with trickle charging - I use trickle charging whenever the battery charge gets low, as determined by how slow the car starts. So I charge it about once a month and it takes a couple of days on thge trickle charge.
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I would just leave it on the maintenance charger. That's how I good care of my rock crawler when it wasn't being driven enough to keep it charged.
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How close is your key fob ? My battery woes stopped when I put my fob into a closed metal contained like an ammo box this blocked the signal to the car actually produced a cheap faraday cage .
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You also buy Faraday bags that are made specially for car key fobs and key rings. My keys are on a Faraday key ring now. They are made to protect your key fob from being scanned which is something car thieves are doing these days. They also have them for smartphones.
I think there’s a Tsb on this issue. If not, check the battery sensor.
Just about all cars now have a parasitic draw when not used. This varies from car to car but is usually in order of 15 mAmp to a max of 50mAmp. So if you have a 55 AmpHr battery, which is a larger one then once it drops below 11V the car basically won't start. This threshold in most batteries is when at about 50% discharge so the calculation is simple :
Amphr of battery X 50% divided by say .015 (ie 15mAmp) = hours until dead. For 55 AmpHr and 15 mAmp that is 76 days, for 50 mAmp parasitic draw about 20 days. For an older battery it is correspondingly less. Typically an alarm system in an older car is one potential culprit, the other is a key fob being sensed
Amphr of battery X 50% divided by say .015 (ie 15mAmp) = hours until dead. For 55 AmpHr and 15 mAmp that is 76 days, for 50 mAmp parasitic draw about 20 days. For an older battery it is correspondingly less. Typically an alarm system in an older car is one potential culprit, the other is a key fob being sensed
Could be a stuck relay .. I had that once, was a/c clutch was always energized. Swapped relays of same part number and found that. Best advice is amp meter between battery and cable, pull fuses to find problem circuit. Remember to leave doors closed and let cabin lights time out.
Be careful about putting battery on charger indefinitely and forgetting about it. Did that and cooked battery, nasty smell filled garage. That said I currently have a charger hooked up on smart outlet and set to run a few hours 3 days a week. I do wonder if battery will discharge thru charger when charger is off.
No there is no reverse current risk when the charger is off
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Tender or trickle chargers are designed and intended to be connected for extended periods of time while boost chargers, designed for stating cars are not. Tender chargers rarely supply more than an amp of current with boosters supply many amps.
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I use Odyssey AGM batteries so have one of their chargers which has modes to charge, maintain (trickle or float charge) and even recondition (desulfide) AGM batteies. It has all sorts of automatic stuff for taking care of batteries too. Their stuff is not cheap but you usually get what you pay for. I didn’t want to to get stuck out in the boonies so I always got good stuff to prevent a long walk out.