We’ve owned 5 Subaru Imprezas now – a Classic MY00 UK Turbo, a WRX 2003, a 2003 STI, a 2004 STI and a 2015 STI and aside from the Classic model, all have suffered the same issue of the battery going flat if the car is left without being driven for more than a couple of weeks. And it seems at least in the UK we’re not alone – a quick search of the various Subaru forums throws up dozens of similar cases.
For example our 2015 STI was just under 6 months old and due to a holiday wasn’t driven for just over 2 weeks – and then failed to start upon our return. Our 2004 STI would consistently have a flat battery if left for 2 weeks or more.
So whats the cause? Too many frequent short journeys not providing long enough to charge the battery properly? A current drain on the battery when parked up? Or maybe just a battery fault? Read on for our thoughts.
Get Your Subaru Professionally Checked Over
The first thing here is to get your Battery and your Subaru’s charging system properly checked out by a reputable garage workshop, preferably one that has some experience with Subarus. They should be able to do a full check on your battery, alternator and charging system to ensure there are no issues causing the flat battery. Assuming all is well, then read on.
Drain from Alarm / Immobilizer
We’ve spent several hours working through the electrical system on both our 2003 STI and our 2015 STI with a multi-meter tool trying to find the cause. Aside from the alarm / immobilizer on the 2003 STI and both the Alarm/Immobilizer and Tracker on the 2015 STI no other current drains were found on either car.
On both the 2003 STI and 2015 STI we removed the car’s battery and had it tested by our battery supplier – and no fault was found on either.
So with nothing found out of the ordinary and obviously not wanting to remove the vehicle’s Alarm system or Tracker, how to resolve?
Subaru’s Smart Alternator
The New Age models onwards of Subaru Impreza (and likely Forester and Legacy) have whats called a Smart Alternator – this effectively means that the battery won’t be charging unless you have a small drain on it whilst driving – for example by driving with sidelights on or interior heater on. It really makes a difference, so if you’ve not tried this give it a go.
Short Journeys?
If you’re using your Subaru for short journeys only – say of around 10 minutes a time or so this could be slowly draining your battery.
By the time the battery’s charge has started been used to start the car, then you’ve driven a short distance and switched off, then repeating again later on in the day – for example short commuting distances to and from your place of work, the battery is never getting a full charge as it would if you were to drive it for longer distances. Over time this will slowly drain the battery and cause starting issues, especially over the winter months, when the Subaru’s cabin heating, lights, stereo, rear window demister etc are in almost constant use the problem is more likely to occur.
Trickle Chargers
If you’ve access to a garage or a covered waterproof lean to or similar its thankfully a fairly easy solution – simply purchase a Battery Trickle Feeder from either our website -we sell the Richbrook version here and most car accessory shops will sell similar for around the same price.
Our 2015 STI is garaged each night and if we’re not going to be using it for a few days, we connect the Richbook product and leave it trickling away looking after the battery. We’ve had no issues of a flat battery since.
Obviously if you’ve not got access to a garage overnight or somewhere at work to keep the battery hooked to a trickle charger then its a little more difficult to resolve this. Maybe you could try simply using a battery conditioner once a month or so when you’re at home during the day to check.
Obviously it goes without saying – follow all basic electric safety guidance when charging your Subaru battery, including keeping all the connections, plugs etc. out of the rain (and water). If you are not competent enough to connect a trickle charger to your Subaru Battery don’t risk trying and ask someone who is.
Does your Subaru Impreza, Forester or Legacy suffer the same issue? Have you managed to resolve it other than using a Battery Trickle Feeder – if so drop us a comment below to let us know below…