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The Random / "Stupid" Questions Thread

Joe_Mama

Autocross Champion

MrFancypants

Autocross Champion
My new battery has died a couple of times so I broke out the multimeter. After driving the car the battery will show a charge of ~12.5 to 12.9. With the car idling it shows the exact same, absolutely no change, even if I cycle various accessories. If I rev it, still no change.

What I don't understand is that I sat and let the car idle for ~25 minutes this morning waiting to pick up a kid, and then the battery was dead. But then if I drive it around the battery charges enough to start it again... but the part that doesn't make sense is that the voltage doesn't show an increase with revs. To ensure the reading wasn't multimeter user error I checked my other car and it showed about 14.0 at idle with high 12s with engine switched off, so I'm using it correctly.

The battery is brand new and holds a steady charge in the healthy battery range. So is my alternator toast?
 
Last edited:

uglybastard

Autocross Champion
My new battery has died a couple of times so I broke out the multimeter. After driving the car the battery will show a charge of ~12.5 to 12.9. With the car idling it shows the exact same, absolutely no change, even if I cycle various accessories. If I rev it, still no change.

What I don't understand is that I sat and let the car idle for ~25 minutes this morning waiting to pick up a kid, and then the battery was dead. But then if I drive it around the battery charges enough to start it again... but the part that doesn't make sense is that the voltage doesn't show an increase with revs. To ensure the reading wasn't multimeter user error I checked my other car and it showed about 14.0 at idle with high 12s with engine switched off, so I'm using it correctly.

The battery is brand new and holds a steady charge in the healthy battery range. So is my alternator toast?
Does anything with the battery installation indicate that it needs to be upright or is it all right that you have it laying flat like you do
 

MrFancypants

Autocross Champion
Does anything with the battery installation indicate that it needs to be upright or is it all right that you have it laying flat like you do
I looked it up and lithum ion batteries apparently can be mounted any way you want.
 

MrFancypants

Autocross Champion
It's four bolts and at the top of the engine. I'm just going to pull it and take it somewhere to have it tested.
 

uglybastard

Autocross Champion
Yeah wasn't sure if liquid inside needed a certain orientation to function.

Check connections and ground, maybe you have a parasitic draw?
 

MrFancypants

Autocross Champion
Yeah wasn't sure if liquid inside needed a certain orientation to function.

Check connections and ground, maybe you have a parasitic draw?
I had that thought too, but I’d think if it were parasitic draw then it would have shown itself on the old battery.

The first thing I checked were the connections to make sure I hadn’t screwed up the install, and they’re all very clean and snug.

All I can come up with is the alternator is putting out enough voltage to keep the battery charged while driving and the old battery was large enough to compensate for low output at idle.

I guess I’ll find out soon, I’ll be on my way to have the alternator tested in a few minutes.
 

torga

Autocross Champion
It's four bolts and at the top of the engine. I'm just going to pull it and take it somewhere to have it tested.

Three of those screws are easy, the last one (lower right) is a huge pain in the ass. Best way I found was to come up from underneath with a flex-head ratcheting box-end.
 

MrFancypants

Autocross Champion
Three of those screws are easy, the last one (lower right) is a huge pain in the ass. Best way I found was to come up from underneath with a flex-head ratcheting box-end.
YUUUUUP

It was made worse by the fact that my fumble fingers dropped my 3/8 13mm socket as well as my entire 1/4 ratchet with 13mm socket. Of course neither fell all the way to the belly pan and the engine just decided that they were theirs.

Anyway, the alternator is good. So that leaves two things... either I didn't connect the auto terminals onto the new battery correctly, which seems like it shouldn't be the case because it's a pretty simple thing to connect, or the battery is just randomly deciding not to charge. I don't know what kind of electronics are in batteries that regulate this, but something is no good.

I'll just email Antigravity support and see what they say.
 

GolNat

Autocross Champion
Does VW have electronic load detection? Honda’s have a system that adjust voltage based off load and different batteries or accessories can throw it off.
 
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