Quick battery question Topic is solved

Post by **Sveedy** » 09 May 2022, 08:42

So it has always been my understanding that an alternator will only charge a battery up to the level it was at when the battery was installed in the car. So if my battery is only at 12v when I connect it to the car, it will only get up to 12v when installed.
So to have proper voltage, I need to charge the battery up to say 14v before installing. Is this correct, or will the alternator actually compensate for the initial low voltage ?

Post by **Sveedy** » 09 May 2022, 10:21

Well a few minutes of googling, and it appears I have been wrong. I guess that unless it's a weak battery, the alternator should bring it back regardless.

Post by **scot850** » 09 May 2022, 10:48

Glad you found your answer. I had never heard of the issue you mentioned in the first post in the thread. The bigger issue in particular in cold climates is short runs and using lots of power drain items like fans on full, rear windshield heater, seat heaters, mirror defrosters, lights and more, where the alternator does not have enough run time to replace what is drained. Over time the battery drains to the point where the car won't start. My wife used to have this issue with a 99 Audi she had in the winter with short runs to the train station.

Neil.

Post by **hausmeister** » 10 May 2022, 02:22

It is also possible the alternator does not supply high enough voltage to fully charge the battery, for that you need around 13.5-14+v. With old wiring/connections, worn brushes etc - if it drops to ~12v it most likely can't fully charge the batttery in any case. My 850 only had 12-12.5v with the above issues.
So make sure this is all working correctly to avoid battery charging issues is my tip.

Post by **abscate** » 10 May 2022, 07:08

Many batteries died during the Covid era. Cars that sat for weeks , especially in cold weather climates, often lost capacity from self discharge , and had to be replaced. I have two low mile cars in the fleet, my rule is if I car doesn’t get used at least once a week It gets a trickle charger installed

My brother got a $900 quote from BMW to replace a weak battery on his ,vert

A $30 battery trickle charger was installed instead

Post by **Sveedy** » 10 May 2022, 08:30

Yes the car came with a nice trickle charger installed, so I use that whenever I think the car might sit for a bit.

Thanks all !