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Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29588
Experience:  GM Grand Master Technician 2007. 14 year experience.
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I am going to flat tow (dinghy tow) my 2015 GMC Sierra

Customer Question

I am going to flat tow (dinghy tow) my 2015 GMC Sierra Denali 2500HD 4WD Diesel (crew cab, standard box) behind my motorhome. Owner's manual says I need to disconnect batteries. Is the concern that the batteries will drain with the key in the ACC position? If so, that is easily addressed. Is there something else to worry about? I dont want the standard GM answer. Need to know if there is a mechanical or engineering reason that the batteries have to be disconnected. Thanks!
Submitted: 2 years ago.
Category: GMC
Expert:  Gm Tech (Cam) replied 2 years ago.

Hi there, I am Cam. This is a legitimate concern. Even in the acc position, some modules will be awake and will drain your batteries in a matter of a day or faster. Add to that, when the vehicle had a couple modules awake and you start moving, it will wake up more and can turn the lights on, accelerating the drain. You will need follow what the manual says for flat towing to ensure the batteries do not drain.

Customer: replied 2 years ago.
if I rig a line from motorhome to charge and maintain the batteries, all should be good. Correct? I have down this on several towed vehicles in the past and have never had a problem.
Expert:  Gm Tech (Cam) replied 2 years ago.

It may work, but also consider the odometer will then likely accumulate mileage as well. Plus it could overtax the charging system on your motorhome. You would be far better to get 2 screw type disconnects or wire in a big battery disconnect switch if you are going to tow often.