Battery dying over night

[iboughtatahoe23]

Hey everyone,


I’m running into a frustrating overnight battery drain on my Tahoe (factory Bose, non-touchscreen, UQA RPO code) and could use some insight from anyone familiar with how these GMT900 trucks handle their electrical networks.


The Setup:


Subs/Box: CT Sounds Tropo dual 10” ported enclosure


Amp: CT-1500.1D monoblock (tuned safely to 30V / ~900W RMS via 40Hz tone)


LOC: CT-LC2 active line output converter tapped straight into all 4 factory sub harness wires.


Remote Turn-on: Tapped into the yellow wire on X14 pin 8 in the MBEC under the dash → LC2 REM IN → jumper from LC2 REM OUT to the amp.


Grounds: Amp is grounded to the rear cupholder stud area; LC2 is grounded to the driver seat bolt.


Battery: Walmart DieHard (brand new this past winter).


The Problem:


System has been running flawlessly for about 3–4 weeks—absolutely hits hard and clean. However, a few days ago the truck started dying overnight. I unhooked my plug-in AFM disabler and dash cam, let the truck sit for just two hours, and came back out to a slow crank. If it sits any longer, it’s completely dead.


The Tricky Part (RVC & RAP):


I know these Tahoes use Regulated Voltage Control (RVC) and Retained Accessory Power (RAP), which makes basic testing a nightmare.


I had the battery and alternator tested on my scanner . It said it tested OK but noted the alternator was "overcharging" (it was hitting around 14.86v) Because of the GM variable voltage system, I know it is completely normal during the ECM's "Startup Mode" to replenish the battery, so I don't think the alternator is actually cooked.


On the RAP side, I do get the normal 10–15 second phantom power-on and a subtle sub thump when opening the doors before starting the vehicle, which tells me the BCM data lines are waking up the factory amp/signals normally.


When the truck is off, the physical blue/red lights on my amp and my bass knob go dark like they should. However, because the BCM data bus can take 10–20 minutes to completely fall asleep, I’m worried something is staying awake quietly or grabbing "ghost voltage" from that MBEC accessory wire.


Before I lock the truck down, clamp the hood latch shut, and perform a 30-minute delayed parasitic draw test with my multimeter across the negative terminal, has anyone experienced a similar issue with an active LOC or the MBEC accessory circuit on these trucks? Could a failing internal sensing circuit in the converter be drawing power silently without triggering the amp's remote line?


Appreciate any advice or experiences with these charging systems!

 

[Foggy]

I know it sounds simple, but make SURE your battery is good.
Load test it ! Double check both battery grounds and positive cable
to starter & fuse block. If the cables are original they may be corroded
internally

 

[Fless]

Test for parasitic draw and you'll be able to figure out what's staying on.

 

[iboughtatahoe23]

I want to walk through the timeline of what happened leading up to the battery failure.


But first I was able to successfully warranty the battery at Walmart with no issues and swapped it right in the parking lot. After installing it, I ran a battery and alternator load test using my Harbor Freight OBD2 scanner. Even though it is a basic $40 to $50 unit, both components checked out completely fine. This leads me to believe the root cause is likely an ongoing parasitic draw.


To give you the exact timeline:


The AFM Disabler: I have been running an AFM disabler plugged into my OBD2 port for years, ever since I got the truck, and it has never caused a single battery issue.


The Dash Cam (2 Months Ago): About two months ago, I installed a dash cam that runs full-time out of the cigarette lighter ports. I intentionally kept it running continuously so it could capture footage and protect the vehicle even when I wasn't in it. I didn't notice any immediate battery issues after installing it.


The Subwoofers (3 Weeks Ago): About three weeks ago, I wired up my subwoofers. The amplifier pushes around 1,000 watts. Before installation, I did my research and confirmed that the factory system should be able to handle this power without needing a 'Big 3' upgrade. I properly prepped my grounds by cleaning the metal down with a steel brush attachment on my drill to ensure a solid connection.


Initially, there were no warning signs—no slow cranking or power issues. This failure seemed to happen completely out of nowhere. The only warning I had was one slightly slow crank leaving work the day before the truck completely refused to start. Because it happened so suddenly, I am not sure if this electrical drain was building up over weeks, or if it is a sudden, major parasitic draw.

 

[iboughtatahoe23]

So the ground to my LOC here is grounded to a bolt in the kick panel. It doesn’t look cleaned up, but I cleaned it up on the back with a file to get bare metal now this might not be a reliable location? I don’t know if this was my issue. And then photo three and four here is where I have the main ground to the amp in the back here over the driver side wheel wheel. Just want to say that whenever I get out of the vehicle, the amp and the LOC shut off like I watched the lights on them shut off and that’s what I wanted to do so that leads me to believe it’s not the subs?

 

[Fless]

Everything's a (educated?) guess until you get an ammeter inline with the negative battery cable and verify the parasitic draw. If there is one, then continue with the appropriate test procedure to figure out which circuit is drawing current when the vehicle should be asleep.

If you don't feel like doing that, a thermal camera might help determine what's hot and what's not.

 

[iboughtatahoe23]

Everything's a (educated?) guess until you get an ammeter inline with the negative battery cable and verify the parasitic draw. If there is one, then continue with the appropriate test procedure to figure out which circuit is drawing current when the vehicle should be asleep.

If you don't feel like doing that, a thermal camera might help determine what's hot and what's not.

Thanks for the advice, Fless. I actually checked the status lights on both the amp and the LOC after the truck sits, and they completely shut down and stay dark, so I'm fairly confident the audio gear isn't staying awake. I also prepped the chassis grounds down to bare shined metal with a wire brush, so the connections are solid.


Honestly, and idk if I mentioned this. I believe there might be a bottleneck with my refurbished alternator I think the real issue might be under the hood during operation. I've noticed lately that if the AC is on full blast and I roll up the windows or use the washer fluid, the blower motor cuts out for a split second. The truck has a refurbished alternator on it right now, so I’m starting to think it just can’t keep up with the vehicle's regular load plus the 1,000-watt amp while I’m driving, leaving the battery slowly starved over time. I'll probably look into upgrading to a high-output unit next.

 

[Joseph Garcia]

Thanks for the advice, Fless. I actually checked the status lights on both the amp and the LOC after the truck sits, and they completely shut down and stay dark, so I'm fairly confident the audio gear isn't staying awake. I also prepped the chassis grounds down to bare shined metal with a wire brush, so the connections are solid.


Honestly, and idk if I mentioned this. I believe there might be a bottleneck with my refurbished alternator I think the real issue might be under the hood during operation. I've noticed lately that if the AC is on full blast and I roll up the windows or use the washer fluid, the blower motor cuts out for a split second. The truck has a refurbished alternator on it right now, so I’m starting to think it just can’t keep up with the vehicle's regular load plus the 1,000-watt amp while I’m driving, leaving the battery slowly starved over time. I'll probably look into upgrading to a high-output unit next.

If your refurbished alternator is working correctly, I don't believe that your issue is related to overloading the alternator with the addition of a 1000 watt audio amplifier. The reality is that your audio system is typically drawing less than 500 watts RMS at any moment, which is the equivalent of about 35 continuous amps. Your AC fans (assuming 500 watt fans) draw about 71 amps at full speed operation. All other amp draws on the truck are relatively small by comparison. I don't know what size alternator you have, but if it is over 140 amps, you still have a lot of available head space in electrical amps capacity.

I believe that your root cause of your issue resides elsewhere, though it could very well still be electrical in nature.

 

[iboughtatahoe23]

As some of you know I currently have my aftermarket audio remote/trigger wire pinned into the switched accessory power at the X14 block under the dash, and it works perfectly. I want to move my dash cam off the constant-on cigarette outlets so it stops draining my battery when parked. This is what @Doubeleive recommended. So wondering if it would work for my dash cam to


Can I splice a 12V female cigarette socket adapter directly into that same X14 switched power circuit that my audio trigger wire is using?


My plan is to hide the female socket under the dash, plug the factory dash cam adapter into it (to drop the power safely from 12V to 5V), and have both the audio gear and the dash cam turn on and off together with the key. Will sharing that switched circuit cause any interference issues with the audio turn-on signal, or is that a safe way to do it?

 

[iboughtatahoe23]

If your refurbished alternator is working correctly, I don't believe that your issue is related to overloading the alternator with the addition of a 1000 watt audio amplifier. The reality is that your audio system is typically drawing less than 500 watts RMS at any moment, which is the equivalent of about 35 continuous amps. Your AC fans (assuming 500 watt fans) draw about 71 amps at full speed operation. All other amp draws on the truck are relatively small by comparison. I don't know what size alternator you have, but if it is over 140 amps, you still have a lot of available head space in electrical amps capacity.

I believe that your root cause of your issue resides elsewhere, though it could very well still be electrical in nature.

If your refurbished alternator is working correctly, I don't believe that your issue is related to overloading the alternator with the addition of a 1000 watt audio amplifier. The reality is that your audio system is typically drawing less than 500 watts RMS at any moment, which is the equivalent of about 35 continuous amps. Your AC fans (assuming 500 watt fans) draw about 71 amps at full speed operation. All other amp draws on the truck are relatively small by comparison. I don't know what size alternator you have, but if it is over 140 amps, you still have a lot of available head space in electrical amps capacity.

I believe that your root cause of your issue resides elsewhere, though it could very well still be electrical in nature.

That math makes total sense on paper, and it’s a relief to know the numbers should technically align. I’m definitely trying to wrap my head around why it's acting the way it is.


The main reason I’m looking closely at the alternator/voltage regulator side of things is a weird glitch I've been dealing with: if the AC is on full blast and I roll up the windows or use the washer fluid, the blower motor physically cuts out for a split second and then kicks right back on. (this was happening last summer too before I even got subs)


Since it's a refurbished unit, do you think it's possible the internal voltage regulator is just lazy or struggling to handle those sudden, stacked spikes at idle, even if the total amperage capacity is technically high enough? I'm just trying to figure out if that kind of momentary voltage drop could be starving the battery over time without showing up as a standard overnight drain.

 

[iboughtatahoe23]

Let me know if I can run any tests with a multimeter. That’s all I got at the moment. Any thing more probably need to go into the shop.

 

[Joseph Garcia]

What are the conditions of your battery cables and alternator to the battery plus terminal cable? They tend to rot from the inside out. You can run a resistance check on these cables. Disconnect both cables from the battery, and then touch the two disconnected cable ends together for about 5 seconds (discharges any capacitors in the electrical system, so that you can make a good resistance check on the battery cables).

Then use your multimeter to check the amount of resistance in all three cables. You should see an Ohm reading of less than 4 Ohms, if each of the cables are good.

 

[jconde]

If your alternator isn't keeping up then the battery wouldn't be fully charged when you turn it off. So after a drive turn it off and check the battery voltage if it's 12.5 or greater that's not your problem.

An ammeter in line is best, but you can just watch voltage as well. If the battery is being killed overnight there should be a noticeable change within an hour, perhaps 15 minutes would be enough. Once you've confirmed that start pulling fuses, starting with the last electrical stuff you added/changed. When the voltage stays steady with all but one fuse pulled you've got your culprit.

 

[Fless]

If your alternator isn't keeping up then the battery wouldn't be fully charged when you turn it off. So after a drive turn it off and check the battery voltage if it's 12.5 or greater that's not your problem.

An ammeter in line is best, but you can just watch voltage as well. If the battery is being killed overnight there should be a noticeable change within an hour, perhaps 15 minutes would be enough. Once you've confirmed that start pulling fuses, starting with the last electrical stuff you added/changed. When the voltage stays steady with all but one fuse pulled you've got your culprit.

Don't pull fuses right away -- just test the voltage drop across the fuse test points. See post #3.