Charging/Battery Issue, not sure what to do next. Help!

Maintenance/Repairs
1

Ok, so here is the problem about 6 months ago, my alternator died just after buying a new battery which, I didn’t notice until the battery had been discharged to 0.

I replaced the alternator, charged, the battery and everything is good, right?

Well no, I’ve noticed the battery seems to discharge really fast. I don’t know if this is because I damaged the battery or I got a bad battery, but like if I leave a door open for like 20min, the battery goes from full charge (12.9v) to like 12.1, sometimes not enough juice to even start the truck.

So I took the battery back to the auto store and got them to test it. They put it on their tester and came to the conclusion the battery is totally fine, no issues at all.

Last night I had it on a trickle charger all night, (2-8amp auto mode) this morning I went to start the truck and it couldn’t even crank, I had to boost the truck and then even though It was running, the truck died a few minutes later because the battery hit 0 again.

I know its not an alternator issue because my multimeter is showing 14v when idling, also it isn’t taking charge from a trickle charger either. I can presume if it was the alternator, the battery would charge fine off the trickle charger.

Is this battery just ruined or could it be some other issue? I don’t want to buy a new battery and just ruin that too? I’m not sure how to further test it? A cranking tester shows ~900 cranking amps but I just can’t keep the battery voltage up. If I hook a booster battery on, the truck comes to life normally so I don’t think its an issue with the starter system. Could this be a grounding issue? (I tested the ground coming off the battery and it seems to work fine, same with the ground by the alternator) Or is it just as simple as this battery is done and the store is lying to avoid a warranty claim?

Thanks for any help. This is on a 2007 Yukon Denali.

2

If the vehicle has the side mount battery cables, peel back the rubber cover of the positive battery terminal and check for corrosion.

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Tester

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3

Hm, unsure, I can try cleaning it, the positive side is certainly dirtier than the negative side, but it doesn’t took super corroded? Should I consider replacing that part fully? (note the red/blue wire is just a multimeter) (Also that multimeter is currently showing 14.6v coming off the trickle charger which is also connected)

I’d also add that if I pull the trickle charger off, the multimeter is showing 12.9v, that is less than an hour after the battery was so low that it could even crank. When it does charge it seems to charge really fast, but also discharge really fast. I’m assuming a corroded terminal would explain charging issues or connection issues to the truck, but it shouldn’t explain the battery going from 12.9 to 12.1 in like 20-30min just off a few cabin lights on unless there is some sort of parasitic drain but if I turn off those cabin lights, it stops draining and if I do a parasitic drain test I don’t see any evidence of parisitic drain.

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4

what is your definition of “no evidence of a parasitic drain” . . . ?

and how long are you leaving the dmm hooked up?

some modules take quite awhile to go to sleep

50 milliamps or less is my definition of “good”

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5

When you replaced the alternator, did you recharge the battery before starting the engine? It is easy to damage a new alternator by overloading it with a discharged battery.

It is rather difficult to damage a battery via a charging cycle.

6

Using a multimeter to check for current when the vehicle is off.

7

Yeah the battery was fully charged when I installed the new alternator.

8

You have only partially answered my question

How many milliamps of parasitic draw are you measuring?