are there any problems with relocating the battery to the rear of the X? I am worried about the heat from the wire being super long? Also, will that increased load be bad for the electrical system or the alt? I am considering running dual batteries as well, multi-batt isolator or system, but I want them in the back vice under the hood. I would also get a bigger alt, mean green is the biggest direct bolt on replacement isn’t it? 180 amp.

I've started my truck off my rear battery before... you just need to have very large cables to the back. I use 4AWG, but I believe these are a bit on the small size, I wish I had ran 2AWG.

I'll be second to reccomend some big @ss wire run back there... at least 2AWG. It's a couple bucks a ft.

Any worries about fumes in the cabin? Isn't a battery box and a vent tube required?(I guess it varies by state)

I (squared) * R losses are your enemy.

As the current rises the square of that current in amps is multiplied by the resistance of the wire which equals ciruit loss disipated in heat.

In free air 4 AWG 75C (167F) wire will hold just 125 amps at 86 degrees. Raise that temperature up to 100 degrees and that current rating drops! The longer the wire the more resistance too. A 2 AWG cable will hold 170 amps again at 86 F.

16 feet of 2 AWG wire will have about 3.21 ohms of resistance at 167 F times the starting current of your motor - say 90 amps squared equals 26,050 watts heating your wires rather than turning your motor. 0.201 ohms per foot.

(dang did I do my math right and does a starter motor use 1000 watts worth of power?)

4 AWG is a worse at 5.13 ohms and 41,600 watts worth of loss along that wire. 0.321 ohms per foot. These loads are just for seconds as the starter motor turns but they're just huge. As temperatures lower below 167 degrees things get better but I don't have reference tables for other than that extreme temperature but still you get the gist.

Reference: Ohms law and Ugly's Electrical References revised 2002 edition.

So why do you want your starter battery in the back anyway?

The factory cables are likely 1/0 or 2/0 and two feet long - 2057 and 82 watts worth of loss/heat. I'd recommend keeping the starter motor in the front putting the isolation solenoid - either mechanical ($15) or solid state ($180) there - and then run cable back to a second battery. I found that the maximum current that my AGM auxillary battery would need to provide if I was running 300 watts worth of lights (25A) and chatting on my ham radio (20A) was 45 amps which can be handled by 8 AWG with 5A to spare.

If my front battery drains I'll stop the winching operation and connect the rear battery to the front to let it recharge the starter battery across time - say ten minutes worth - before isolating the batteries and starting the truck up off the starter battery to continue to let the alternator charge the front battery. I'd then connect the two batteries together to recharge the rear battery. Isolate again and then commence to winching once more. Repeat as needed.

Adding a $600 180A alternator would help but not too much. You want to limit the charges on AGM batteries as much as possible as too many rapid discharges/recharges on your $250 battery are going to kill it straight up. There are special AGM batteries used in UPS units which are high-amperage but they're not built like the typical yellow- or red-top batteries.

Paul (retired Master Chief Electrician's Mate USN)

Here's my dual battery set up (on the cheap).

http://thenewx.org/forum/showthread.php?t=9671

There was no real reason for me to want to put them both back there, other than I didn't know if the alt would have a problem with trying to charge two batts and one of them being much farther away than the other? The isolators are just big diodes aren't they? So wouldn't the load from the extra wire and the voltage drop from the diode cause the power to travel MORE to the path of least resistance? I mean we are talking several feet difference in wire length, once all is said and done. (Maybe I am just sleepy, pretty long days lately?)

I do like the idea of having at least one in the back though. I have seen someone jump another car off with their Crysler 300C (battery in the trunk) Much easier for them to just back up to you on the side of the road vice turning around or pulling up beside them. That and I have my amps for my stereo in the back. Not to mention I will be buying my bumper and winch (finally) once I get back from Iraq, so getting rid of some weight in the front would be nice.

Guess one in front and one in back would just leave me with more options when it comes time for wiring lights and releys and cb and car-puter and so on...

Thank you all for the wisdom

I moved mine to the back and used 2ott(sp?) welding cable. Welding cable is nice because it is flexible.