I have a 2015 2.5 OB , and for the last few months when I am at a red light, foot on the brake the RPM will drop to around 625-650 and the headlights will flicker. When I was following behind the other night, all of the rear lights will also flicker and pulse. I had the dealer look at it, and of course they said nothing is wrong. Anyone seen this before? Any ideas?
I popped the tops to the cells on the battery, and tested each with a batter acid tester. They all checked out fine, hooked my battery charger to it, it put some juice in it for like 5 minutes and said it was fine.
Just another wild guess here but your alternator might be over charging at idle. This would cook the battery and cause acid boiling out the top and could cause lower idle. If voltage monitor circuit is bad, bad ground somewhere, bad diodes in alternator, list goes on as to what might cause over charging but that is where I would tell them to check next. This is definitely a warranty issue.
I went ahead and picked up a battery. Interesting that the battery from Subaru and its rated for 356 CCA, when you look up in interstates book, it says OEM needs 490CCA. I think Subaru undersized the battery by quite a bit, I have never need a car battery that small.
If you have a charging problem you will damage your new battery. Larger battery is a good idea anyway, however. For some reason the 2.5 comes with a small battery, the 3.6R comes with a 490cca.