Battery Charger Pulsing?

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77
Location
AL
Drove my truck last Saturday night with no problems. Didn't drive the truck at all on Sunday or Monday. Went to crank it this morning and the battery was dead. I recently installed an AFM delete module on it, but I've let it sit for 3 or 4 days and had no issues, even with the AFM module plugged in the whole time. Okay, so I unplugged the AFM module and put the truck on my battery charger, 2 Amp charge rate setting. Went out about 2 hours later, and the ammeter gauge was pulsing between 4 Amps and 6 Amps, and the battery wasn't accepting charging. I checked the connections to be sure they were good, even repositioning them, and the battery charger still pulsates. The battery is a Carquest Gold with a manufacturing date of 07/18. Thoughts?
 

Auae85

Thread starter
Messages
77
Location
AL
Battery charger is an old Schumacher SE-82-6 12V dual rate charger. I inherited it from from my step-granddad over 20 years ago, and no telling how long he had it. I have charged a lot of batteries with it, and never seen this behavior before.
 
Messages
35,864
Location
ME
It could be a car computer/ relay trying to boot up now that the battery shows some voltage. If your battery is flat it would take a 10 amp charge, easily. They're around 80 amp-hours so if you want to drive it this week, use the faster mode. Next time you have your charger on a full battery, turn on your headlights. You'll see the current draw on the charger's ammeter. The mode switch on buzz-box style chargers is pretty crude, as they like to say, YMMV. The bad battery is certainly a possibility as well.
 
Messages
2,790
Location
USA
Disconnect the battery from the truck electrical system. Charge for a couple of hours then measure the battery voltage. If it is stuck at less than 12 while charging, the battery has an internal short and needs to be replaced.
 
Messages
2,790
Location
USA
On a basic manual charger, the amp meter going up is good proof that it is working. The amp meter going higher than the nominal rated current means that something connected to the output is holding down the output voltage-- totally run down battery (which should resolve with charging for a time), defective battery, or load from the vehicle system. The amp meter will normally fluctuate slightly with changes in the input line voltage, since there is no voltage or current regulator in the charger.
 
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Auae85

Thread starter
Messages
77
Location
AL
Thanks for the replies. I will check the battery charger on a known good battery to observe the ammeter, and I will try to charge the battery when it is disconnected from the truck. May have to wait a day or two due to work commitments and since we're starting to get some outer rain bands from the hurricane.
 
Messages
202
Location
MI
The vehicle is trying to wake up and the charger can't supply enough current - this is very bad for electronics. Disconnect the battery before connecting the charger.
 

Auae85

Thread starter
Messages
77
Location
AL
Well, thankfully all we got was slight winds and about 1-1/2 inches of rain from the hurricane since we were northwest of the main force. Anyway, yesterday afternoon I removed the battery from the truck and put in on the battery charger. No pulsing of the ammeter. I checked the voltage just prior to this, and it was approximately 4.61 volts. I left it on the charger for several hours and took it off last night before bed. Battery was now at 12.22 volts. Before leaving for work this morning, I checked it again, and it had dropped to 11.88 volts. I will check it when i get home to see if it has dropped any further.
 

Auae85

Thread starter
Messages
77
Location
AL
BW, battery chager seemd to be working fine with no noises or odd smells.
 
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Auae85

Thread starter
Messages
77
Location
AL
Checked when I got home and it was approximately 11.5 volts. Had it on the charger since then; I'll disconnect the charger and check the voltage before going to bed, and then check it again in the morning.
 

Auae85

Thread starter
Messages
77
Location
AL
Battery was at 13.17 volts when I went to bed, and 12.88 this morning. I took it to a parts store to have it checked; they did and said it was fine (passed the load test). Okay, reinstalled in the truck and drove around some today, with no problems. I'll watch it over the next few days. The truck is a 2009 GMC Sierra with 5.3L, and it has the adaptive charging system, so I may go get it tested just to be sure.
 
Messages
35,864
Location
ME
If you're checking the battery immediately after disconnecting the charger you'll get a falsely positive high reading. That said I think the battery's toasted. Dropping to 4 volts is not good.
 
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