What kills a battery in 6 hours?

rocketman4321 · Post by **rocketman4321** » 16 Jul 2017, 15:07

I was working under the car a bit this a.m.--backed it up, drove it on the ramps, drove it back off a half hour later. On a lark, I measured the battery voltage after that, which was 12.44V -- pretty typical, and it's had a series of short trips this week. Key was removed. Six hours later, car won't start. Voltage at the battery terminals is 7.65 volts connected, about 7.8 open circuit. I measured a drain of ~0.2 A, but that might not be reliable at such a low voltage. Battery appears to be taking a charge normally.

Anybody seen something like this? We did have an incident a while back where my daughter ran the blower for 15 min and then the car wouldn't start, but an hour later it was mysteriously fine. No repeat of that since. Battery was load tested (a couple times) OK.
I'll start digging when the battery's back up, but any ideas are appreciated.

Thanks!

Post by **abscate** » 16 Jul 2017, 15:32

You would need a 10 to 15 amp draw to discharge a battery in 6 hours.

That should not be hard to find

rocketman4321 · Post by **rocketman4321** » 16 Jul 2017, 19:13

I agree. Unfortunately, it's gone. After charging the battery, the parasitic draw was about 130 mA (on a 10A range on the DVM). This fell to ~ 50 mA (forgot to write it down) after several minutes and/or cycling the key position. It jumps to 1.2A after opening the door, which is normal.

I absolutely cannot remove the key without this low level of draw. Push/pull/wiggle--the switch seems solid. In position 1, it's about 690-800 mA (radio off). Position 2, of course, overloads the meter. I also tried every electrical thing I did this a.m.--brake lights (500-ish mA), windows up and down, etc. The right rear window is a little sticky but it runs and the key switch would still rule.

One oddity: when I first connect the battery, the clock/trip display turns on every segment, and the "icy road" warning light is lit. This goes away after maybe 45 seconds, and the clock is displayed as expected. Is this normal?

I'll watch the battery overnight, but it seems like a (sigh) intermittent failure. My wife is already asking when we're getting rid of the car--this comes on the heels of a MAF failure a couple weeks ago. Need a smoking gun. Anybody had a relay stick closed?

Post by **abscate** » 16 Jul 2017, 19:38

How old is the battery? It could have an internal short and not hold a charge

A car repair bill is always cheaper than a car payment. It easy to forget this when the repair bills are due.

Post by **jreed** » 17 Jul 2017, 05:08

Last weekend I had a battery fail in about 5 minutes... from cranking, starting and running apparently normally to no-crank/no-start.
The battery developed an internal fault that caused high internal resistance when under heavy load -- maybe a crack in a post, weld or some other mechanical fault. When not under load the battery read normal open voltage. I wrote up how I tracked it down with an analog load tester here:

viewtopic.php?t=81897

rocketman4321 · Post by **rocketman4321** » 17 Jul 2017, 18:07

It's a good suggestion--I was also thinking maybe a cell or two shorted. However, the symptoms are a little different than yours. Mine read 7.8 volts with the ground wire disconnected--definitely open-circuit. After charging and reconnecting (and a dozen more connection cycles looking for drain and operating the windows and lights) it was fine. Did two short trips today OK. Of course, that doesn't necessarily preclude an intermittent mechanical fault. And it would possibly explain the fault a couple months ago when it left my daughter sit, and then started fine an hour later.

After that, I had the battery load tested (twice) at Adv Auto--it's one of their "gold" ones. Fine both times. I have not tried one of the capacitance-type testers. But again, a mechanical failure could be intermittent. Battery is 4 years old.

Post by **scot850** » 17 Jul 2017, 21:05

One issue that I have heard of is a fault with the alternator, but more specifically the voltage regulator. Can't recall the specifics, and electrical stuff is not my forte, but it was an alternator problem allowing the alternator to drain the battery very quickly with the engine switched off.

Neil.

Post by **850 LPT** » 18 Jul 2017, 10:56

My electrical knowledge is very limited, so I don't know if this could even be related to your problem. But I had a parasitic draw once on my old 850 that stemmed from a bad glove compartment switch. Seems to be a common problem on these cars. I hooked up an ammeter and pulled the fuse for that circuit to confirm.

Post by **abscate** » 18 Jul 2017, 11:18

Mine read 7.8 volts with the ground wire disconnected--definitely open-circuit.

Something is fishy near in a country near Denmark..

A battery that is reading only 8ish Volts has big problems - a discharged battery will still read 11.5-12.0 Volts with no current capacity.

The clever way to answer the glove light box version of the 'tree in the forest' problem is to shoot an iPhone movie in your glove box as you close it. Much to clever for me to think up, I have stood on the shoulders of giant trees as they fell in the forest.

rocketman4321 · Post by **rocketman4321** » 19 Jul 2017, 21:13

I pulled the glovebox light a while ago just to be safe. And it draws milliamps, not the 10-12 amps needed here. I agree it kills many of these cars if it has more time to drain.

The very low voltage did seem fishy--thought at first I had a shorted cell. But it would take multiple dead cells, and the "smart" charger didn't squawk--just charged it right up.

Car has remained fine since Sunday on short/local trips.