Battery draws down after 24 hours

[Orpedcrow]

X2. I'd have it load tested even if the resting voltage looks OK. Most auto parts stores will do it for free.

Fer sure, I’ve tested batteries at 12.5 volts but had a bad cell.

 

[df2x4]

I'm not sure what the factory spec for resting current draw at the battery is on these trucks, but it might be in the '99 factory service manual somewhere. @The_Family_Tahoe if you haven't already, you can download the GM factory service manuals for your '99 here in searchable PDF form for free. Post #77, this link should take you right to them.

https://www.gmt400.com/threads/88-98-service-manuals.43575/post-1234512

 

[RichLo]

Agree'd with the suspect battery.

Voltage isnt always the best way to tell if a batt is bad or not, if it read 9v then yea, it has some bad cells. Otherwise a Load tester is the best way to check a battery...

Advance Auto Parts - Down for Maintenance

shop.advanceautoparts.com

Sometimes if a battery just slowly goes weak you can do multiple charge/discharge cycles with that load tester to bring it back around but you need a charger that has at least 40amps to get enough heat into it to dissolve the lead sulfate on the cells. And you need a load tester like the one in that link, that one has a coil that builds heat to discharge the battery. Those little electronic units dont draw enough power for long enough to drain a battery low enough to let it charge at 40+ amps.

Edit: if anybody does try this, do it outside on the ground with a breeze, it will most likely off-gas Hydrogen and can accumulate and pop if you do it in an engine bay or in a still garage.

 

[HotWheelsBurban]

We took the crew cab to Sam's club and they swapped out the battery (but they said they checked it 3 times and it showed good). Maybe so, but I know what the voltmeter said yesterday. So we went out to Stafford and caught my friend at O'Reilly's and had one of their coworkers check the truck out with the store's test equipment (my friend was already supposed to be gone for the day but had stayed a little late). Their tests showed the battery and alternator were good; alternator is putting out over 13 volts and the gauge is indicating that. So it seems like a possibility that I have a current draw somewhere, if the truck sits a couple days....
So I will just undo the ground cable every evening till I can figure out what it is. It's supposed to rain all day tomorrow so we probably won't be going anywhere then ....
Is it possible that the relay for the power locks could be doing this? There does seem to be some correlation between the locks working properly and battery power( or lack thereof?).

 

[Schurkey]

Their tests showed the battery and alternator were good; alternator is putting out over 13 volts and the gauge is indicating that.

WHAT "tests"? There's a heap of 'em, and they're all needed. I'd be especially interested in alternator AC voltage, sometimes called "ripple".

I'd have expected over 14 volts from the alternator, assuming the battery is reasonably charged.

So it seems like a possibility that I have a current draw somewhere, if the truck sits a couple days....
So I will just undo the ground cable every evening till I can figure out what it is.

Seems likely. Check it with a multimeter. Most multimeters are fused at 10 amps, some will take 20 amps "short term". The fuses for my multimeter are hatefully expensive, so I really don't want to pop 'em. Any drain of more than 1/2 amp (0.5 amps) is excessive after the computer goes to sleep after the ignition is off, doors are all shut, lights are out, and ~30 seconds goes by. Lower amperage is better.

Is it possible that the relay for the power locks could be doing this? There does seem to be some correlation between the locks working properly and battery power( or lack thereof?).

I suppose. Pull the fuse for the power locks and see what happens.

 

[HotWheelsBurban]

WHAT "tests"? There's a heap of 'em, and they're all needed. I'd be especially interested in alternator AC voltage, sometimes called "ripple".

I'd have expected over 14 volts from the alternator, assuming the battery is reasonably charged.


Seems likely. Check it with a multimeter. Most multimeters are fused at 10 amps, some will take 20 amps "short term". The fuses for my multimeter are hatefully expensive, so I really don't want to pop 'em. Any drain of more than 1/2 amp (0.5 amps) is excessive after the computer goes to sleep after the ignition is off, doors are all shut, lights are out, and ~30 seconds goes by. Lower amperage is better.


I suppose. Pull the fuse for the power locks and see what happens.

They don't have a fuse, it's a circuit breaker. This is a '97 truck, built in late September '96.

 

[HotWheelsBurban]

WHAT "tests"? There's a heap of 'em, and they're all needed. I'd be especially interested in alternator AC voltage, sometimes called "ripple".

I'd have expected over 14 volts from the alternator, assuming the battery is reasonably charged.


Seems likely. Check it with a multimeter. Most multimeters are fused at 10 amps, some will take 20 amps "short term". The fuses for my multimeter are hatefully expensive, so I really don't want to pop 'em. Any drain of more than 1/2 amp (0.5 amps) is excessive after the computer goes to sleep after the ignition is off, doors are all shut, lights are out, and ~30 seconds goes by. Lower amperage is better.


I suppose. Pull the fuse for the power locks and see what happens.

The alternator was reading 13.9 volts, I saw the reading.

 

[Schurkey]

They don't have a fuse, it's a circuit breaker. This is a '97 truck, built in late September '96.

Fine. Pull the circuit breaker, see what happens.

 

[Just Nobody]

The alternator diode(s) could have shorted; that would not be affected by the fuses.

However, I'd also expect higher amperage draw. I don't worry about parasitic drains under about 0.2 amps. I'm not sure of your meter reading--you're saying you have a drain of .014 mA? Or .014 A?

Are you sure the battery is not self-discharging via the conductive slime that builds-up on the case? CLEAN the battery case.

Disconnect both battery cables, FULLY charge the battery so that it has 12.6--12.7 volts AFTER it's been off the charger for an hour. (It'll maybe have 13+ volts when fully charged and fresh off the charger.) See what happens.

The battery may be plain ol' defective, unable to hold a charge.

This has happened three times to me.

 

[The_Family_Tahoe]

I charged the battery up and tested it at 12.9 volts. I let it sit one day disconnected and tested it again at 12.0 volts.
I'll get the battery tested at with a machine that applies load, but it seems like 12.0 would be enough after one day of sitting to crank the starter.