Car Doctor Q&A: My Subie’s Battery Keeps Going Dead

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Subaru in particular has had battery discharge issues over the last few years, but this is a problem that’s coming up with more and more cars, now that the electrical system is under such high demand.

Q. My 2017 Subaru Forester is having problems with the battery. On one of the many road service calls that I put in, the AAA guy tested the battery and alternator and said everything was fine. He also tested to see if there is anything drawing the battery down and didn’t find anything.

I’ve had to jump start the car at least six times in the last month. We drive it every day, not far but every day, so I would think the battery is getting recharged. There’s a ton of complaints on the internet and Subaru is doing absolutely nothing.

I’m afraid to buy a new battery and have the same issue! Any suggestions?

A. You mentioned that you drive your car every day, if the trips are short the battery may not be getting fully recharged. Years back I had a representative on my radio program from AC-Delco and they told me that the average car after being started takes about seven miles of driving to recharge the battery.

In an older car, the charging system works as soon as the car started, but the charging system in late model Subaru vehicles doesn’t work all of the time. By limiting alternator output there is less load on the engine which helps improve fuel economy.

Older cars would also almost completely shut down nearly every electrical system in the car when the key was turned off. This is not the case in modern automobiles. In addition to memory functions for the radio, seats and clock, there are several computer controlled systems that can take time to shut down.

It is my understanding that Subaru has come up with an updated charging system profile that adds additional charging time. In addition Subaru customers have told me that some dealers have installed batteries with a higher electrical reserve that helps with any “normal” parasitic drain.

Some other things to consider: batteries today — as good as they are — don’t “cycle” very well. If the battery in your car has been completely discharged six times, chances are it is not in very good condition even though it is only two years old. Also the battery when it is discharged should be recharged with a battery charger set on a low rate. The charging system in a car is designed to maintain a battery not completely recharge it. Using a battery charger set on two amperes could take six hours to fully recharged a battery. It is also important to make sure all other accessories are off (parking lights, courtesy lights).

One final thing, keep the key fob away from the car. As you approach your car the computer recognizes the key fob and starts turning some systems on. If the key fob is in the car or close proximity to the car some systems will not shut down and the battery will become more quickly discharged.