2nd battery in Mercedes - supplement power/alternative to cell link

abrown3mtg

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My 2010 E550 is a 4matic. As such, the battery is under the hood. I was curious if I could add a second full sized battery in the trunk where the rwd models have one. My thoughts behind this is I live in a cold climate, do make a number of short trips, have a hardwired radar detector, aftermarket sub and amp, and now plan to hardwire a dual dash cam. I can buy one of the cell link b or blackvue batteries, but for roughly the same cost, I could add a full second agm. I know running the wiring will be somewhat time consuming but I am able to do so myself. The camera will run when triggered as I'm sick of door dings and scrapes and the associated costs of fixing them.

  • I'm curious if there is a downside to going this route. Will charging be compromised/excessive strain put on the alternator? Would I be less likely to recharge when driving?

    What are your thoughts on upside vs downsides?

    Thank you!
    __________________
    2010 E550 4matic Sport P2.
    Mods: Staggered 20" Gunmetal Niche Misano's for summer, Escorts 9500ci with laser shifters, lowered with STAR, Blacked out grill and logos, flat badge, JL Audio 12w6 and 500/1, E63 Meisterschaft exhaust (quad tip), OE Tuned
 
if it's done right with a dual battery isolator to handle the switching/charging and a good AGM or deep cycle battery then yes it can be a much better solution
 
AGM batteries don't like being emptied so you need something to turn it off at half empty, even deep cycle lead acid batteries will last a lot longer if you don't empty them.

Don't underestimate the cost of the cabling, an AGM battery can take a huge charging current when it is nearly empty, cables to run the length of the car will not be cheap and you need cables that wont drop molten copper and burning insulation on top of your fuel tank! You also need to mount the battery properly so that it can't take your head off in an accident, there is a good reason bullets are made of lead - it's not easy to stop!

On the other hand, lithium batteries don't mind being emptied as long as they are not left empty for a long time and the charging current is limited by the charge controller so it doesn't need thick cables and wont put heavy loads on your alternator, but has the disadvantage that if you only drive for 20 minutes in a day it probably wont last for 24 hours recording.
 
+1 Jokin- IMHO it's the best possible solution but I'd consider a wet-cell deep-cycle (if the RWD models use a wet-cell battery) or a SLA as those are more robust against deep discharging. And you should be able to get factory parts for mounting the battery which would ensure crash-protection was correct. For the heavy-gauge wiring you can use jumper cables sans the clamp ends as long as it isn't exposed to heat. These have heavy insulation and always cost less that the same gauge of standard wire with much thinner insulation. I run a 30A circuit to the back of my work-vans with this stuff and have had no problems in 5+ years. Given the heavy charging current, solder the connections and terminals instead of only crimping them.

Even 4 cams 24/7 don't really need a lot of battery capacity, but batteries don't like to be deeply discharged so go for 2X capacity or more of what you will be drawing and the battery will last a lot longer. This also give you the benefit of extra run-time should you be parked for longer than planned.

Phil
 
If you want a quality dual battery setup i can link you the parts needed but its cheaper and simpler to get a Celllink to be honest.

Dual battery setups is popular in 4wding and cars with beefy sound systems (no headlight dimming). The alternator will handle the load just fine, with an isolator setup for example it doesnt charge both batteries simultanously, it charges your starter battery first then once full it goes over to the second battery.

I've got a 100Ah AGM secondary battery which can run my fridge for a couple of days at camp (or indefnitely with the solar panel hooked up)

if it's done right with a dual battery isolator to handle the switching/charging and a good AGM or deep cycle battery then yes it can be a much better solution

Sadly new cars have variable voltage alternators, they will start up at 14.4v~ but once the engine is warm it drops down to 13.2v~. This makes VSR isolators unsuitable because batteries need 14.4v to reach full charge, plus having long cable to the back of the car causes a voltage drop.

So to get around this you need to use a DC-DC charger instead like a Redarc BCDC1225LV or CTEK D250S. These will bump up the voltage and give it a nice multi-stage charge.
 
If you have the parts lists flip9 that would be amazing! I had dual batteries in my Jeep TJ, f350 diesel (dual alt), As well as my buggy but didn't have to set up any of them. I know there are "kits" out there but am confident for the same price or less I can piece together the best possible kit/solution. Fortunately a very close friend of mine owns an auto repair business. He has battery cable that was purchased in bulk and fits the bill $$ wise. There is already a direct path through the firewall and a channel in the tub of the car where the factory cables would be run. I'm going to be pulling a portion of the interior apart to upgrade my laser jammers to Alps in the next few weeks and it would be a pretty ideal time to kill 2 birds with 1 stone. I can get a proper AGM battery for around 100-120 at shop cost, another 20-30 for cables and connectors, so the Isolator is the wildcard. If I needed to go with a Redarc BCDC1225LV or CTEK D250S 220-650 usd, that would be a deal breaker for me and I'd skip that option.

I totally see the utilities in the cell link b or blackvue batteries as a turn key easy plug and play option, however, (especially in cold climates), I just don't see the potential for the capacity that is desired.
 
First you need to check what type of alternator you have by driving around till the car hits operating temps (15-20min drive) and then check the battery voltage with a multimeter. If its reads around 13.4v then its too low to charge a secondary battery so you will need a DC-DC charger.

For DC-DC setup you will need:
- AGM battery
- CTEK D250S DC-DC Charger - http://a.co/84XOKPX
- 6 AWG wire or thicker (about 25ft) - http://a.co/hENr4VN
- Battery post terminals - http://a.co/daawuU1
- 12x Ring terminals/Lugs + heatshrink - http://a.co/2meI3DB
- 2x Inline fuse holders or circuit breaker (30A fuses) - http://a.co/6ZMzHh6

Optional:
-Split loom tubing (extra protection for the wires) - http://a.co/ckfmD1I
-6way fuse block (for power distribution) - http://a.co/3cy9OIL

These are just examples i searched on amazon. Im not sure what DC-DC chargers are available in the US market so have a search around. I'm sure you can find cheaper and better alternatives from your friend.

The wiring is simple, just run the wires to the back where the charger and AGM sit next to each other. Theres also an option to add thin flexible solar panels as the CTEK has a built-in MPPT controller.

dual%20battery.png
 
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