I am getting back into my GS build after a long break. Unfortunately my battery is toast and won't take a charge. I have relocated mine to the trunk and always felt that the crank was too weak, and also due to my build/tune it takes a bit of cranking to get the engine fired up. I was always dealing with a weak or insufficient crank even with a new battery. I am considering putting the highest cca battery I can find in, or maybe even dual batteries for the capacity to crank for a long time, or if the car sits for a while. I was running a Deka Intimidator AGM 850cca and it was not as sufficient as I hoped. I am thinking two Optima "yellow tops" for their deep cycle and high cca. I have a high amp DC alternator installed too, so plenty of power to keep the system charged.
I hate the idea of the weight of two batteries, but at least they will be over the rear wheels. And with a 800hp goal I probably don't need to worry as much about weight as I have in the past with most my builds anyways. Looking for suggestions or ideas of how to best upgrade my cranking power. Any reason the car would not like dual batteries? Or is there a good single battery that is up to snuff? I am running huge 0 gauge wires. So I don't feel like it's lacking in other ways. I may also benefit form a upgraded reduction starter if they make them for this car. Ideas welcome.

 

I also relocated my battery to the trunk. You have to remember that with DC, direct current, you lose amperage thru the cables, that’s why it feels weak. One the main reasons I wanted to relocate my battery was specifically so I can use a larger battery to increase the power for my stereo. So you want use the largest battery possible, either budget wise or whatever will fit in your mounting location? Any car that came with the battery in the trunk, like all Mercedes and BMW, use a Group H, you can get an H5, H6, H7, H8 and H9. I am running an H9, it’s rated at 900CCA, about the maximum output possible on a 12V battery. That’s what comes in all full-size German sedans. But its actually than a stock GS needs, you could probably go with an H7. It’s highly recommended that you get an AGM Battery, they won’t splash with battery acid if you ever get rear ended or something and bad luck makes it a nightmare. Also all H Series batteries have are built with a breather port so you can vent outside of the trunk which will help avoid some other possible issues like fumes building up in the car while you’re driving

 

As an electrical engineer, you’re correct. It’s called voltage drop due to the added distance of the cables. My S-class uses at 65 pound H9 battery.

 

I found an H9 size from Braille that is 1100 cca in the $550 range. I can get two 800 cca Optima "red tops" for around $275 each, run in parallel would be 1,600 cca for about the same price. Yellow tops are around $15 more each. Undecided if I would benefit from them. All I really need is cranking power which is what the red tops are for. Of course I'd have to switch out my tray for a dual tray, and wires/terminals for the dual setup. But I think that is sounding good. 1,600 cca would be nice and I've seen Optimas last 10 plus years in service.

 

Optima batteries keep getting sold, the last few I bought weren’t worth ****. I have an Odyssey, it’s Aout 5 years old and has been flawless, I have heard of Braille, they have a good reputation, but I don’t know for sure on that brand. How come your wanting so muc battery power? If your have a High Output Alternator, and 1 H9, and you should be able to supply some serious electrical output. Another battery would supply power for longer periods when
the engine isn’t running, but once your charging system is running, you shouldn’t need a 2nd battery? Or what are you planning to do?

 

My battery always ran out of juice too quick. For years it tested fine, well over the 850 cca rating actually. It just takes a lot of cranking, and the relocation to the trunk makes it worse. My issue is tuning and the injectors I'm running I think and some very cold spark plugs. They work, but the way they fuel on cold start is pretty bad. I have big fuel pumps I have to let run with the key on for a bit too, gauges start up, wide band oxygen sensors have to heat up, two ECU's and all the added sensors etc. The car runs the stupid ABS pump during this time. I would have to plan when I was going to use the car, charge it up first, otherwise listen to the cranking get weaker and weaker until it either starts if I'm lucky, or goes flat. One thing I noticed is when the battery was fully recharged, the cranking was much faster and it would start easier. Keeping it in that state required constant charging or always using a jumper. So I think I would be better off with a huge amount of cca.

 

You know what you should do, running a battery in the OEM spot that can give your starter a good source of power close by. You would just need something like this.

 

That's a good idea. However I have used that area for my oil catch can, AEM ECU, and a few lines and wires etc. I removed the tray and everything. I have plenty of room in the spare tire well for a second battery, however I am still undecided on this. It's a very expensive route to put two new AGM batteries in. I could do a single H7 (94r) to save a lot of money. I'm sure the size alone would be an increase in overall capacity. The Deka is only a group 35.

 

Honestly it just sounds like high impedance from your battery relocation.

• Did you do the 'big 3' upgrade (alternator charge, starter power, battery ground)?
• Did you run both a positive and ground cable all the way to the engine bay, or just a positive?

My battery relocation in my 2jz mk3 supra-

• 2/0ga + and - from battery in the hatch to the engine bay
• Water proof distribution blocks in engine bay for both + and -
• 4ga starter + from distribution block
• 4ga alternator charge to distribution block
• 2/0ga ground from battery to chassis in hatch
• 2 extra grounding straps from the engine block to the chassis
• Haltech ECU gets dedicated, clean + and - directly to battery

This will take a lot of unnecessary load off of your electrical system. Battery relocations are really tough on it. This setup gave me great spark, charge, cranking, and clean sensor signals for my ECU

 

I only ran positive from the back. Grounded to the body in the trunk though. I believe I put a thicker ground from the block to frame. I will look into that. I ended up purchasing a AGM 94r which is substantially larger than the last group 34 battery I had. I also bought a Noco trickle charger too. I think this time around it will go better if I practice good battery maintenance. Should allow for strong and long cranks if necessary, and the last battery should have lasted a lot longer, but I let it go dead too many time sand sit that way. The trickle charger should greatly extend the life and also keep max cranking power ready to go.

 

On my 92 SC400, I get a pretty labored crank the first start in the morning, waa...waa....waaa...Vroom! like its about to start clicking but after that first start, it kicks over like a new battery, di-di--vroom! . The battery IS NEW! My wife thinks its the 32 year old starter, jeez I hope not under the intake. Maybe just to contacts? Im thinking if it kicks over so fast after its warm, why the cold start blues? It only gets 50F here at night year long. Battery is an Interstate 850CCA larger than stock CCA as the stock size seems to not be available anymore.

 

Built your own Lithium cells.
https://batteryhookup.com/products/1...v-48ah-1-23kwh