I have searched and read many, many old threads on this topic and really don't understand - why not trunk mount the battery?

Every classic I have owned did not have a battery under the hood. I have always used zero gauge cable and proper (overkill) grounding-battery to frame-frame to firewall-engine to firewall...

I do not understand the remote solenoid, or the junction block. My batteries have always been grounded to the frame, and the positive cable ran right to the starter. I have never had a charging issue or starting issues with any of my trunk mount installs. What difference does it make if the cable is 3' from the starter to battery, or 12'?

Am I missing something in these old threads, or is there REALLY some reason not to trunk mount a battery for street applications?

As always thanks for any advice or 'heads up!'

The reason to mount the battery in the trunk is for weight transfer. Otherwise there is no good reason other than the look.

Starters pull lots of amperage. 200 Amps isn't out of the norm and a seized motor can pull as much as 900 Amps. Resistance is the enemy. I'm not sure what the resistance rating of zero gauge cable is, but let's say it's 0.001 ohms per foot. The numbers aren't important (cuz they're probably wrong), but they'll illustrate the point.

A 3' piece would have a resistance of 0.003 ohms. A 12' piece would have a resistance of 0.012 ohms. Now, at 200 amps, the 3' piece would drop 0.6 volts. The 12' piece would drop 2.4 volts. Most starters start to crap out about about 8 volts. Also, the batteries internal resistance will cause it to drop a couple of volts during a crank cycle. So all of a sudden, your 12 volt battery is putting out 10 volts during a crank. Take away 2.4 volts for the 12' of wire (actually almost double because of the ground return path resistance) and your starter is seeing about 7.6 volts.

Long story short, trunk mounted batteries can be made to work - there are several folks on this board that have done it. To me, it seems like too much of a headache and expense unless you need that extra 8lbs of weight over the right rear wheel to hook up at the track.

I am still not sure that much is lost. I would like to know the exact number.

Most car batteries weigh in the 35 - 40 lb range, so for weight distribution it can be a factor. Every BMW my wife and I have owned have a rear mounted battery as well.

A stock battery cable is around 4' in my camaro. The trunk mounted will be around 10'. <I just measured>

I would like to find out just how bad the pull is, but once again - I have had zero problems with my other classics.

I must also admit. I get the battery out from under the hood mainly for appearance purposes. I will post pics of my under hood in a couple of weeks, so you can see why.

There is nothing wrong with a properly engineered trunk mounted battery.

IMost car batteries weigh in the 35 - 40 lb range, so for weight distribution it can be a factor. Every BMW my wife and I have owned have a rear mounted battery as well.

I must also admit. I get the battery out from under the hood mainly for appearance purposes. I will post pics of my under hood in a couple of weeks, so you can see why.BMW has placed the battery in the trunk for the reason of maintaining a 50/50 weight balance, along with other weight reducing/relocation ideas.

Drive a nose-heavy car and it plows into the corner, goes straight instead of turning. Drive a rear heavy car and it will turn around 180* in a turn. A 50/50 car is balanced, goes where you point it, to a certain extent, speed entering the corner is one of them, or something like this, I'm not a road racer, so I'll be off into the trees........

Placing the battery in the trunk is a racing idea, for any racing, whether it be for drag, oval, or rally. Once again, trying to maintain a 50/50 weight balance for rally racing, location of weight in oval, such as place it on the left of centerline of the car to make those left hand turns easier, and in drag racing for momentum, as mentioned earlier.

Battery has weight, and placing it at different lengths from the rear axle is another adjustment the driver has, depending on the track surface. Loose track, move battery to the furthest rear point to maximize the momentum, remember the weight and longer lever? Sticky track, move battery closer to the rear axle, less momentum. Physics happening. Or, as you do, to clean up the engine bay.

I used 00 AWG cable and solder-potted the terminal lugs on. From battery post to solenoid post, I lose 1.5 volts. As dnult states, cable resistance is important, and so is the cable temperature. Temp goes up, resistance goes up, less current flows. Physics thing happening. As JimM states, nothing wrong with a properly engineered trunk mounted battery.

If you're running an internal regulated alternator, ideally you would like the sense wire on the positive battery post, or as close to it as you can get. Remember, you have to charge it back up after starting. You can do the same thing with an external regulated alternator, remote sense it. Run the sense from the battery post rather than from the igniton switch, the brown/white wire.

I put my battery in the trunk to clean up the engine compartment and for the weight transfer/imbalance issues. I used the MAD Enterprises system where the 2/0ga main battery cable is hot only when cranking and 8ga wires are run for charging and power up to the accessories. It works great, and looks good.
The only problem is constantly answering the question: "What is that blue box in the trunk"?

The stock location for my battery in my '72 Vette is behind the drivers seat. Plenty of room under the hood, so I assume GM put it there for weight distribution.

So, you just run your sense wire adjacent to the battery wire forward to the engine compartment?

Yes I do want the handling aspect of the weight transfer as well. I didn't put in the TVS kit, AGR steering box, SFC, new X-brace, new bushings, and all new steering linkage (not to mention all the aluminum on the engine) to go in a straight line.

Thanks for all the advice!

So, you just run your sense wire adjacent to the battery wire forward to the engine compartment?I would think you would want the sense line as close as to the battery as can be.

Normal hook-up for the sense line is at the load, but now the battery is relocated further away, and voltage drop of the cable, battery post would be good and the added length of cable is the reason for relocating the sense line.

Maybe I'm being too picky about it, but when comes to the final round and you're called to the line, I want to be able to fire it up and compete, not sit and pray to the Start God to start. One less variable to think about.

However, I'm sure you could get away with a firewall connection, such as the solenoid post.

You want the sense wire close to the real load, which is the fuse box/junction point where all the electrical accessories hook up, so you'll have full voltage to these items. Aside from the few minutes of recharge to the battery after you start the car, there is very little current going to the battery, maybe an amp or two.