Battery Tender causes horn to honk

[JohnH4260]

Just took delivery of my 2021 Sierra Denali Saturday (3/20/2021). Problem I m having is when connected to my Battery Tender the horn goes off every few hours. To stop the honking, I have to push the lock button on the key fob. I’ve got the positive clamp connected directly to the positive battery terminal and negative clamp connected to the body ground which is on the frame next to the battery. The vehicle is locked in the garage with the hood up. The honking usually happens 4-6 hours after connecting the Battery Tender, then happens every 3-4 hours afterwards. 
 

Immediately after the horn begins honking, I receive a text message from Onstar stating: “OnStar: 2021 Sierra theft alarm activated. Call OnStar 888-466-7827  or 911 if an emergency. Do not approach vehicle unless safe. Txt STOP to cancel.”

 

I went out this morning at 5:30 and the battery tender shows a fully charged battery (solid green light). I’m thinking after becoming fully charged, the Battery Tender goes into sleep mode. Then after a few hours, it goes back into trickle charge mode, and this is when the horn starts honking. And the theft alarm is activated.

 

Is there any way to prevent this from happening? Maybe keep the hood closed? 

[mafd2]

Why are you using a battery tender?

[ericarenee]

I have this exact same thing happen on my  2004 express van that has a Lo jack like tracking anti theft after market device. The installation company told me the Battery Tender  charges the battery full. Goes off then a few hours later will come back on and starts Discharging the Battery   slightly then  goes back into charging state .. During the Discharge state on the battery tender the Alarm system senses a battery Drain.  The only solution for my Van . which is much older is to NOT Lock the Van. This causes that part of the Alarm System to not active. Since its a aftermarket alarm  I am not sure if this will work for you are not. It is possible the hood open might be triggering it as well. 

 

I only use the battery tender on the Van when  the temps drop super cold out and I use it because i have a Heating pad in a compartment in the back where i Keep  Tool Batteries , Caulking and things that need to stay above freezing. If you need a battery tender on a Brand new Truck all while stored inside your garage you might wanna take it in to be serviced . 

 

Just my Opinion  

[JohnH4260]

34 minutes ago, mafd2 said:

Why are you using a battery tender?

I use a Battery Tender on all my vehicles to maintain the battery since 1997. Never had a problem until this week. 

[JohnH4260]

Opps, double post. 

Edited March 25, 2021 by JohnH4260
Double post.

[diyer2]

I would hook negative to battery post and lower hood, but not latch it.

[Gangly]

51 minutes ago, diyer2 said:

I would hook negative to battery post and lower hood, but not latch it.

[mafd2]

1 hour ago, JohnH4260 said:

I use a Battery Tender on all my vehicles to maintain the battery since 1997. Never had a problem until this week. 

No need to run a battery tender.  These batteries stay charged for many many weeks without being started.  

[IlliniST]

Maybe because the hood is up?  I'm sure there is an alarm and indicator for that on the DIC.  

 

Try shutting the hood (and not pinching the Tender) and see if that fixes it.

 

 

EDIT - Just saw you asked about running with the hood closed in your last line.  Yes, I'm sure that's it.

 

Edited March 23, 2021 by IlliniST

[Steve-2019]

Or you could do what I do.  I also use Battery Tenders (Deltran) on all my vehicles for the last 20 years with no issues.

 

I  plug in my Battery Tender into my current Silverado (and all my previous Silverado) 12V receptacle at the back of the center console and run the cable out one of the rear doors.  No issues ever using this method.  

[508gm1]

I have a CTEK tender on my 2017. Never had an issue with the theft system activating. The hood is slightly open on mine, doors are never locked, but it is inside. The truck can sit for many months with no use (about 5 months right now). The tender is directly on the -ve & +ve battery post.

Edited March 23, 2021 by 508gm1

[Cuse]

My 2020 had been on life support (Deltran Battery Tender) for about 5 months while stored for the winter. Doors not locked, hood closed, and hooked directly to the battery. No issues with the horn or anything else.

[brianf60]

I'm just throwing this out there. If the suggestions for hood/ door locks don't help you may want to try other models of battery tenders. Many of the more sophisticated ones I have looked at have m multiple charging strategies intended to help revive damaged batteries. This usually involves pulsing the voltage output in some form or another. This may be causing issues with how some of the vehicles modules function. 

[JohnH4260]

Problem solved. Park in garage; Leave hood open; Plug in Battery Tender; Remove metal key from key FOB; Lock doors with metal key and the vehicle alarm system will not arm. Battery Tender now functions and alarm is not activated.

[2016 Sierra Owner]

On 3/23/2021 at 9:30 AM, diyer2 said:

I would hook negative to battery post and lower hood, but not latch it.

If you don't latch it the system still thinks the hood is open anyway. The closed switch is built into the latch.