Discharged Battery - Trust the Parts Guy or Mud? (1 Viewer)

[car-car]

So, was camping in Pismo this weekend for Surf 'n Turf. Got packed up Sunday morning and truck wouldn't start. Symptoms of a drained battery. Jumped it from another 80, and it started up first time. Scangauge showed voltage around 15 once it started as it tried to recharge the battery, and then settle in the normal mid to high 13 range. Let it idle for about a half hour, and then drove for about an hour. Stopped twice (once for gas, once for lunch). Started back up no problem each time and then drove straight home for about four hours. No issues. On Monday, started right up in the morning, but was a little weak in the evening, but it started and drove home with no issue. But then it started being an issue.

Yesterday (Tuesday), it wouldn't start in the morning (dome lights and dash lights were dim, and didn't have enough juice to attempt to crank). Grabbed a battery on the way home to drop in, but then I started wondering if maybe there was an issue with charging system or maybe a parasitic drain that might be draining the battery. I didn't want to drop in the new battery until I was sure it was just the battery. On the existing battery, I took a reading on the battery posts with the mulitmeter, and it registered around 8.2, which would explain why it wouldn't start. I jumped the old battery in the truck (again, turned first crank on the jump) and drove over to the local parts store that does free tests on batteries and charging systems. I had them run tests on the battery and charging system. They said the battery was fine, but there was a problem with the charging system (guy was saying it seemed to him like a bad rectifier in the alternator). Something didn't quite make sense. Drove it home and broke out the multimeter to get some quick readings. With it still running in the driveway, scangauge was reading voltage of 13.7 and I was getting a reading on the battery posts of 13.6 (so, fairly close readings). Turned off the ignition, and it was reading 12.6 on the posts. So that seemed okay.

Fast forward to this morning, grabbed the multimeter to get a reading before I even attempted to start it, and it was at 8.4, so something definitely isn't right.


So, after that short novel, I am looking at the following conclusions:

• The charging system might be okay after all (I don't see how a bad alternator can be charging the battery when the engine is running since it runs fine once I jump it, and then is draining the battery once the engine is off).
• Battery is toast and won't hold a charge, despite the diagnosis of the parts store guy's test (this would be the easiest fix, and I plan to replace with the new one, but I don't want to ruin the new battery if there is another problem elsewhere)
• There is some kind of major parasitic drain that has just come up that is putting a pretty major drain on the battery (taking it from 12.6 to 8.4 in a matter of about 9 hours of sitting seems pretty extreme)

Let me know what you guys think would be my best plan of attack. I trust you guys a lot more than the guy behind the parts counter.

Thanks.

 

[e9999]

from what you describe the alternator appears to be fine (good voltage and keeping the battery up). With rather either the battery bad or a big drain.
If you have an ammeter or a good multimeter, easy to check for the latter first. (Put it on high amp setting first.) That way you would not overdischarge a new battery, which is not good if it's a starting battery. (But would be likely fine if it's a dual purpose or a deep cycle one.) Or just put the new starting charged battery in and keep track of voltage with time without engine running. Stop if you see it going quick below 12V. That is easy to do, would tell you probably all you need to know and would not lead to new battery damage.
Or charge the old battery, disconnect the truck wires and put a big load on it, like a spotlight, and see what happens.
If it's a good battery, is charged, and goes to 8V in a few hours, we're talking major drain. Headlights kinda drain. That should be easy to find (and could be dangerous too if not found). Unlikely.
Some of the above easier to do if you have a separate charger.

Lots of fun to be had...

My bet is a bad battery. How old is it?

 

[Diskord]

Ditto, bad battery.

Charge your existing battery (or use the new battery), disconnect the pos, and hook up an amp meter inline to see what kind of drain you have just sitting with everything off?

 

[TeCKis300]

It's the battery.

Deep cycling is really punishing on the battery. The deeper and longer it's been discharged, the more permanent the damage. The recent colder weather will also expose a weak and damaged battery more readily.

 

[Brentbba]

x2 on how old the battery is. If it's beyond 5 years, replace it anyway. Good Luck Adam!

 

[car-car]

Thanks for all the input and ideas from everyone. I will put these tests to work when I get home this evening.

I'll definitely be replacing the battery, since I am not sure of its age, but I'm guessing its past its prime. I'll take a look at the date stamp on it when I get home.

I just didn't want to mess up the nice shiny new battery if there was something else going on in there.

Thanks again, and I will report back on the progress this evening.

 

[car-car]

Bonus points to those who said bad battery. Swapped in the new one, and it seems to be holding at 12.4 and no sign of any parasitic drain after several hours. Oh, and the battery was an '08, so it was time for a new one.

Thanks again for the input and ideas.

 

[sdnative]

Glad you got it figured out, and it was just the battery. Which one did you end up going with?

 

[1973Guppie]

I have had this happen a couple of times, the parts stores do a load test but not for a distance of time. Meaning they check if the battery takes a load and charges, that's it. I have had several batteries take that load and then slowly lose it over a few hours.

Noah