Car audio battery upgrade
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Joined: May 2024
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From: Northern Indiana
2014 c300 w204.080 3.5 v6
Car audio battery upgrade
Hi all
So I'm thinking of running a battery in the trunk for my Sub amp to help with slight light dimming.
My question is has anyone added a large battery to the trunk and charged it from the Aux battery in the trunk?
I'm thinking trying to keep both battery's meaning the Aux battery already there and the battery I'm going to add. Is this how most do it?
Or should I remove the Aux battery and just replace it with a large battery?
I dont use the trunk so looks dont matter at all to me. Just dont wanna overload the Aux battery circuit with a larger battery if its gonna be a problem.
Thanks for any advice at all
RobertR728
So I'm thinking of running a battery in the trunk for my Sub amp to help with slight light dimming.
My question is has anyone added a large battery to the trunk and charged it from the Aux battery in the trunk?
I'm thinking trying to keep both battery's meaning the Aux battery already there and the battery I'm going to add. Is this how most do it?
Or should I remove the Aux battery and just replace it with a large battery?
I dont use the trunk so looks dont matter at all to me. Just dont wanna overload the Aux battery circuit with a larger battery if its gonna be a problem.
Thanks for any advice at all
RobertR728
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2021 GLB250 FWD, 2023 GLA250 FWD, 2013 C250, 2015 GLK350, 2005 ML350SE, 2003 E320
My 2013 had a battery holder in the spare tire well sized for an H-7 battery. I would imagine that’s still there on the 2014. All it needed was a tie-down strap. I don’t see any reason to keep the aux battery after installing the full sized one as long as it just replaces it directly in the circuit. Since the aux battery is a SLA and isn’t vented, you may want to look into venting the new battery to the outside.
Thread Starter
Super Member
Joined: May 2024
Posts: 505
Likes: 123
From: Northern Indiana
2014 c300 w204.080 3.5 v6
Thanks Old Piggy I was thinking about the fumes too and prolly a sealed battery would be best. I've also come across this Battery/Capacitor combo that may fit my needs but I've got to do some reading about these.
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2021 GLB250 FWD, 2023 GLA250 FWD, 2013 C250, 2015 GLK350, 2005 ML350SE, 2003 E320
FYI - My grandson used a 1Farad capacitor + 24F battery + isolator in his pickup. Before installing that, the sub amp was killing the alternator. You probably don’t need the isolator.
My granddaughter uses only two 1Farad capacitors without the extra battery in her W206 supplying a 1kW amp and two 12” subs.
Me, I just listen to the 60W radio in the head unit.
My granddaughter uses only two 1Farad capacitors without the extra battery in her W206 supplying a 1kW amp and two 12” subs.
Me, I just listen to the 60W radio in the head unit.
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From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
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2021 GLB250 FWD, 2023 GLA250 FWD, 2013 C250, 2015 GLK350, 2005 ML350SE, 2003 E320
I played in a rock band in the late 60s… Birds don’t sing in my world. If it doesn’t get louder than the crickets in my head, it doesn’t exist. Even then it’s just noise. I can feel the subs but I can’t actually hear them. I’m the last surviving member. But hey, just being able to get upright in the AM is good. 😉
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W212 MY'14 M276-3.5NA @75kMi
hydrogen vented out
My 2013 had a battery holder in the spare tire well sized for an H-7 battery. I would imagine that’s still there on the 2014. All it needed was a tie-down strap. I don’t see any reason to keep the aux battery after installing the full sized one as long as it just replaces it directly in the circuit. Since the aux battery is a SLA and isn’t vented, you may want to look into venting the new battery to the outside.
Last edited by CaliBenzDriver; Jan 16, 2026 at 05:41 PM.
