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since i couldn't find youtube or pics from any threads here, i'd like to offer mine ... hope it helps someone ... for my MY 2013 GL450, the aux battery was not next to the main battery under passenger seat before they moved it to the passenger rear cargo ... although I can touch, from the side cargo compartment, the metal housing/cradle holding the aux battery (would've been 1,000,000 percent easier access) I could not access the aux battery itself except from the opposite side, which is why i had to go through and pulled back the felt covering the wheelwell and it was a ***** as I did NOT want to remove the whole felt, just enough to access (removing the gray plastic bracket would've made life 100% easier, but that was not worth removing other panels) ... there is only ONE, bolt that holds the bracket encasing the aux battery to the metal housing/cradle and it has to be removed from inside the cradle, the nut portion, not separate piece, is part of the cradle itself (seriously engineers???) so yes, i had to slide my whole hand with the socket to unscrew the bolt) ... yes, the duracel battery from batteries plus is slight smaller and +/- terminals reversed ... but so far no battery errors on dashboard ... hope this helps someone
Last edited by vivaitalia; Jun 8, 2020 at 10:16 AM.
I am getting ready to replace this battery myself, on the same vehicle. I thought I had seen a Youtoob video where they did access if from inside, where the spare tire etc, resides. Have to L@@K again, i guess. I suppose it's too much to ask for it to be a simple, quick task.
Here video show where battery locate on 2013-2016 GL450 it Auxiliary battery not main battery because main battery is probably under the passenger seat. Engrish not grape but looky where and not hard to replace after all. Good luck. I have no idea what this auxiliary battery does, but I get messages saying aux battery not working, so time to replace just to make the GL450 be happy. LoL
Last edited by tonylinc; Apr 30, 2025 at 07:15 PM.
I was getting a message on the dash about the auxiliary battery failing. So I finally replaced the little battery, and there was little chance of getting the bracket back in that holds the battery in place, so I cut a piece of the foam insulation (Once you access the battery you'll see this foam piece three inches thick by about a foot square) I cut a little piece off that, to stuff in there to hold the battery in place so it won't move around. All back together and the thing I noticed: There's an option - I dunno if all GL450s have it, but when sitting at a red light, instead of holding the brake pedal all the time until the light turns green, you can press the brake pedal once again and the dash says HOLD and you can let go of the brake. Once the light turns green again, you just step on the gas pedal and take off. That was the one thing that had quit working when that battery quit. So, that's one of the things it does. There's also a "P" in a little blue square that indicates the vehicle is running its "Program" mode, to make a beep sound if the vehicle thinks you could possibly crash. That also, was not activating any more, with the old aux battery. I know that not all GL450s have this option because when I went to get a new windshield, the fools at the glass place kept getting the "wrong glass" because I have "all the electronics" at the top of the windshield, and they were getting glass that was for versions that weren't so fitted. Finally to get the right windshield, I had to go thru a MBZ dealership, since their computers, will know the exact glass that's right for this vehicle. I have no idea what other things this little battery does. The one that came out of the car, was original. I imagine 12 years is about this battery's lifespan. It's a sealed, lead-acid battery.
I was getting a message on the dash about the auxiliary battery failing. So I finally replaced the little battery, and there was little chance of getting the bracket back in that holds the battery in place, so I cut a piece of the foam insulation (Once you access the battery you'll see this foam piece three inches thick by about a foot square) I cut a little piece off that, to stuff in there to hold the battery in place so it won't move around. All back together and the thing I noticed: There's an option - I dunno if all GL450s have it, but when sitting at a red light, instead of holding the brake pedal all the time until the light turns green, you can press the brake pedal once again and the dash says HOLD and you can let go of the brake. Once the light turns green again, you just step on the gas pedal and take off. That was the one thing that had quit working when that battery quit. So, that's one of the things it does. There's also a "P" in a little blue square that indicates the vehicle is running its "Program" mode, to make a beep sound if the vehicle thinks you could possibly crash. That also, was not activating any more, with the old aux battery. I know that not all GL450s have this option because when I went to get a new windshield, the fools at the glass place kept getting the "wrong glass" because I have "all the electronics" at the top of the windshield, and they were getting glass that was for versions that weren't so fitted. Finally to get the right windshield, I had to go thru a MBZ dealership, since their computers, will know the exact glass that's right for this vehicle. I have no idea what other things this little battery does. The one that came out of the car, was original. I imagine 12 years is about this battery's lifespan. It's a sealed, lead-acid battery.
The hold has been on many MB models : ), MB doesn't advertise it so sadly people don't know about it. It is not as obvious as a hold button on the centre console for example that other makes have.
The blue P is the parking assist was it not? It detects a parking spot and shows if it is ready to self park with an arrow? Do you mind posting a picture?
The aux battery also affects the shifting behaviour (transmission), the GL doesn't have it I guess but on newer models, it is also responsible for the auto start/stop function.
The aux battery is also meant to store things in memory in case the 12V battery is not working at all, so such memory in certain modules don't get erased.
I actually prefer MB having the brake hold being activated by pressing the brake pedal once coming to a stop because other makes, the auto hold button keeps it on all the time until you press the button. MB's is so easy! Sometimes you want to have it off during the journey and on many times.
2013 GL450, 2023 Tesla Model Y LR, 2024 Outback L XT
I never had the pleasure of experiencing the brake HOLD feature in my GL. The Tesla obviously has it and my Outback has it also. I thought it was just not available in the 2013/2014 GL models. Now I am intrigued and want to replace the aux battery even though no msg in instrument cluster about the AUX battery malfunction.
I never had the pleasure of experiencing the brake HOLD feature in my GL. The Tesla obviously has it and my Outback has it also. I thought it was just not available in the 2013/2014 GL models. Now I am intrigued and want to replace the aux battery even though no msg in instrument cluster about the AUX battery malfunction.
How many years has the aux battery been in the vehicle? If similar to OP's that's a good run.
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