My thoughts:  

Putting the engine cranking battery further away from the starter system degrades the voltage available and limits your amps available for cold cranking.  

I have volt meters in the cockpit for both batteries, with voltage readings taken at the main buss input.  I have one Odyssey battery on the firewall with 12.8V showing cold (engine off) and the other (equally charged) behind the firewall with 11.5V (and sometimes lower if sitting longer); a 1.3V drop over 6 feet of wires.  Unless you run copper (not aluminum) wires and make it thick gauge (adding substantial weight), you will have lousy voltage up front for crank if the battery is in the back area.

You should be replacing that cranking battery every three to five years anyway.  $130.  You'll spend more than that on heavy wiring or FBO power supplements.

Jeff L
LIVP



From: "Greenbacks, UnLtd." <N4ZQ@VERIZON.NET>
Subject: Re: Odyssey PC680 Batteries on Firewall -- Cool Enough?
Date: October 21, 2013 2:30:43 PM EDT
To: "Lancair Mailing List" <lml@lancaironline.net>


Hi Valin,

Move your hydraulic pump from its current location.
Create a small bulkhead and put the pump directly behind your seat.
The reasons are too numerous to list!
Don't even think twice about making this change.
Equally important, locate your pump breaker within easy reach on your panel.

Angier Ames
N4ZQ
69hrs