A general search for battery temperature sensor at O'Reilly. I haven't messed around with this before, but I have read about it. General to the industry, there is a known thing, which is to give more charge to the battery when it is cold, and not just when turning the starter, because batteries don't have as much voltage when they are colder.Some cars have a temperature sensor underneath the battery (Chrysler products)... I am not sure that Subaru does.
I do know that some newer Subaru has a CURRENT sensor on the battery-negative terminal. The computer will boost alternator output based on electrical load.
Some common electrical loads which will increase alternator output:
- Cold ambient temperatures demands more battery power hence increases this temporary alternator boost
I have a voltage gauge, and I watch it all the time. When I start my car cold, it goes over 14v for a little while, like 10 minutes. After that, I expect to see less - sometimes 13.2v. Sometimes, when I'm drawing more with my stuff, down to 12.6v or so. But a cold start gives me 10-15 minutes of higher voltage, more current.
Another approach to tricking out my charging system is to install a diode in the voltage sense line from the battery to the alternator. This would drop it by a half a volt, and trick the alternator to make more charge for the battery. It's just that I thought I might be able to fool the thing another way, if I could make it think it was still cold.