aux battery
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From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
aux battery
my wife's 2016 e350 4matic wagon just had its main battery die completely. went from working perfectly, to totally dead after being parked a day and a half. 6 hours on a 10 amp charger and it was still at the first blinky on the NOCO Genius 10. Couldn't start it with my Noco Boost Plus, either, but it started right up on my truck jumper cables (16 feet of AWG 2 copper, ooomph!). battery store determined battery was indeed totally dead. This batt was the Mercedes branded battery the selling dealer put in the car before we bought it in 2020, so its 5 years old, time for a new one. new Duracell group 48 AGM, and it started on the first tap of the start/stop button.
thinking the aux battery is likely stuffed too. I know I can find 'generic' AGMs with the right size and contacts but not sure if they have the correct specs (12V 12AH 200A) or a vent tube. most batts that size are 12V 18AH or 20AH, and I'm not sure the max current. what all do you guys use ? FCP sells the Mercedes branded batt
thinking the aux battery is likely stuffed too. I know I can find 'generic' AGMs with the right size and contacts but not sure if they have the correct specs (12V 12AH 200A) or a vent tube. most batts that size are 12V 18AH or 20AH, and I'm not sure the max current. what all do you guys use ? FCP sells the Mercedes branded batt
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W212 MY'14 M276-3.5NA @75kMi
TWO DEAD BATTS
I'd go with the genuine MB from FCP 
The price difference may not be worth running around.
My AUX is doing exceptionally well doing nothing at 10Yrs mark. Warranty replaced at 6Mo.
A batt Main drain is a double sentence with AUX backuping up its power.
I hope your wife's batteries stop getting fast drained.
Try Reboot + Float as a form of protection.
The price difference may not be worth running around.
My AUX is doing exceptionally well doing nothing at 10Yrs mark. Warranty replaced at 6Mo.
A batt Main drain is a double sentence with AUX backuping up its power.
I hope your wife's batteries stop getting fast drained.
Try Reboot + Float as a form of protection.
Last edited by CaliBenzDriver; Jul 21, 2025 at 09:00 PM.
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
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From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
I've found my local Batteries Plus store has Duracell brand AUX14 AGM batt that seems to meet all the specs... But I'll probably pull the original and bring it to their store to do a load test.
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From: par·a·dise
2012 E63 Wagon
I've always been an Interstate guy and purchase an MTX/48H8 main battery every 4-5 years. Last year I spoke to the Interstate distributor while he was delivering batteries to my dealer. When I inquired about the Interstate MTX-AUX14 Auxiliary offering, both said the lead time is excessive and they never sell them.
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From: In the Shadow of the Tetons
2013 ML350 Bluetec
Your auxiliary battery is big enough to need venting? The only ones I've seen are small - think burglar alarm sized - and have 1/4" tabs for terminals. They can be mounted upside down without caring.
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From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
They are VRLA (Valve Regulated Lead Acid), also called AGM (Absorbed Glass Mat). *NORMALLY* they don't vent, but under unusual conditions, like severe overcharge or overheating, the safety valve can open, and they vent. AUX14 AGM batteries are 5-7/8: x 3-7/16 x 5-3/4 inches. Size of a medium-large motorcycle battery, they use M6 screws for the terminals.
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> The dashboard battery is only used once to lock tranmy in Parking position.
> The facelift AUX is used as a chassis back-up power during engine crank in ECO cycles. It sees deep cycle and gets unlimited charge current.
Bosch ECU designer must have expected flammable hydrogen off gazing...
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From: Baltimore County, MD
'13 s212 63 p30. '06 LX470
I'd go with the genuine MB from FCP
The price difference may not be worth running around.
My AUX is doing exceptionally well doing nothing at 10Yrs mark. Warranty replaced at 6Mo.
A batt Main drain is a double sentence with AUX backuping up its power.
I hope your wife's batteries stop getting fast drained.
Try Reboot + Float as a form of protection.
The price difference may not be worth running around.
My AUX is doing exceptionally well doing nothing at 10Yrs mark. Warranty replaced at 6Mo.
A batt Main drain is a double sentence with AUX backuping up its power.
I hope your wife's batteries stop getting fast drained.
Try Reboot + Float as a form of protection.
Op, did you try those Noco chargers on a forced charge? When the battery is too low, the chargers won’t work. You can either get some energy into it by running it to another battery first and letting it stabilize or using the forced charge option. I know you’re all good now, but in case this happens again due to some sort of draw on the battery.
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From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
the noco saw the battery and auto identified it as a AGM, and started a charge cycle, the battery was just sucking down the juice and not charging.
VRLA batteries only vent hydrogen if they go into an over-pressure situation, which typically happens if they are forcably over-charged, or short circuit sorts of loads. I've used VRLA batteries in all sorts of applications for decades now, and not had one blow a seal yet.
VRLA batteries only vent hydrogen if they go into an over-pressure situation, which typically happens if they are forcably over-charged, or short circuit sorts of loads. I've used VRLA batteries in all sorts of applications for decades now, and not had one blow a seal yet.
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NO PLATE CAPACITY
the noco saw the battery and auto identified it as a AGM, and started a charge cycle, the battery was just sucking down the juice and not charging.
VRLA batteries only vent hydrogen if they go into an over-pressure situation, which typically happens if they are forcably over-charged, or short circuit sorts of loads. I've used VRLA batteries in all sorts of applications for decades now, and not had one blow a seal yet.
VRLA batteries only vent hydrogen if they go into an over-pressure situation, which typically happens if they are forcably over-charged, or short circuit sorts of loads. I've used VRLA batteries in all sorts of applications for decades now, and not had one blow a seal yet.
Their capacity gets extremely reduced.
They end up with NO capacity to charge or discharge from sulfated plates.
Last edited by CaliBenzDriver; Jul 22, 2025 at 08:24 PM.
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From: Baltimore County, MD
'13 s212 63 p30. '06 LX470
the noco saw the battery and auto identified it as a AGM, and started a charge cycle, the battery was just sucking down the juice and not charging.
VRLA batteries only vent hydrogen if they go into an over-pressure situation, which typically happens if they are forcably over-charged, or short circuit sorts of loads. I've used VRLA batteries in all sorts of applications for decades now, and not had one blow a seal yet.
VRLA batteries only vent hydrogen if they go into an over-pressure situation, which typically happens if they are forcably over-charged, or short circuit sorts of loads. I've used VRLA batteries in all sorts of applications for decades now, and not had one blow a seal yet.
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From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
I've always been an Interstate guy and purchase an MTX/48H8 main battery every 4-5 years. Last year I spoke to the Interstate distributor while he was delivering batteries to my dealer. When I inquired about the Interstate MTX-AUX14 Auxiliary offering, both said the lead time is excessive and they never sell them.
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Gotcha, Was asking about the noco because I have a booster and a charger, and have never done the force charge but I have used another battery to bring up the charge so that the charger would charge. In that instance I was truly seeing what benefit desulfating the 12 yr old aux battery would make. The battery lasted about two days after desulfation and recharge.
I didn't try the force mode, as the regular auto charge mode was pumping 10A into the battery, the battery just wasn't taking the charge, suggesting maybe a shorted cell or something. Frankly, its my wife's car, she drives to San Francisco at night with a friend or two to go to the SF Opera, and I don't wany any problems, the main battery was 5+ years old, I got her a new battery. a day or two later, eco start/stop is working fine, and no aux battery errors are showing up, so we'll leave the aux battery along until it starts to error, THEN I plan on getting an AUX14 from a local supplier.
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yeah, I have a Panasonic 12V 20AH VRLA here that is pretty much dead. its about 10 years old, for the last 6-8 years it has been hooked up to a car stereo in a wooden box with powerpole connectors on the back, speaker connectors (using guitar plugs) on the side, and an antenna connector on top. The boombox is getting upgraded soon to having a LFP 12V 10AH, and a DC-DC LFP charger module, plus the older panasonic car stereo gets swapped for a newer one that has bluetooth just because I have it here. this mostly serves as an FM radio at an annual bluegrass/folk festival where they broadcast everything on pirate radio so you can listen in camp.
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2016 E350 Sport
I bought this one from Batteries Plus 3 years ago. No problems at all.
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BLUE GRASS RULES
yeah, I have a Panasonic 12V 20AH VRLA here that is pretty much dead. its about 10 years old, for the last 6-8 years it has been hooked up to a car stereo in a wooden box with powerpole connectors on the back, speaker connectors (using guitar plugs) on the side, and an antenna connector on top. The boombox is getting upgraded soon to having a LFP 12V 10AH, and a DC-DC LFP charger module, plus the older panasonic car stereo gets swapped for a newer one that has bluetooth just because I have it here. this mostly serves as an FM radio at an annual bluegrass/folk festival where they broadcast everything on pirate radio so you can listen in camp.
you may be familiar with called "Bluegrass Signal"
Bluegrass Signal website https://www.bgsignal.com/
that's where I discovered the legend: Bill Monroe.
Last edited by CaliBenzDriver; Jul 23, 2025 at 12:35 PM.
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I lived in the North Bay in the early 70s, but down here on Monterey Bay, we don't get any SF area FM stations...
not exactly bluegrass, but last night we saw Dave Alvin & Jimmy Dale Gilmore at a local small club. I videoed a few snippets of it
not exactly bluegrass, but last night we saw Dave Alvin & Jimmy Dale Gilmore at a local small club. I videoed a few snippets of it
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From: near Birmingham, AL
2014 E350 Sedan; 2025 GLB 250
I have a post-face lift model and after getting the "Auxillary Battery Malfunction" error, I found an unvented Interstate battery in the trunk. I took it to Auto Zone and they sold me a Diehard battery with the vent hole. $155.
