Adding a Second Battery

I have a 2003 gmc sierra and i need to install a second battery there is a spot passenger side for it i was wondering the best way to wire it because i need the second battery for my snow plow

thanks

I made a dual battery charging system for my motorcycles and scooters so I never have to worry about the start battery failing due to accessory power draw.  I use the Odessey PC-680 (AGM Type Battery) as the aux. or House battery.  Used a  system designed for boating from BEP Marine that incorporates three switches and a VOLTAGE SENCING RELAY to charge the Aux. / House battery when the alternator is putting out 13.8 volts or better. That way my start battery is always charged up first. 

I mounted the battery and charging system in a UM-1 size battery box commonly used in trolling motor applications for fishing boats.  Used a quick disconnect plug (50 amp) between the start battery and the dual battery charging system in the battery box so I can move it between my vehicles.  I'm making a fuse box that incorporates quick disconnect harness from DEL CITY ELECTRIC SUPPLY (toll free: 800-654-4757) which has 3 ea 12ga wires and 5 ea. 16 ga. wires.  A harness with matching quick disconnect plug delivers fused circuits to the front and another one delivers fused power to the rear of the bikes and scooters.

The Odessey PC 680 is a dual purpose battery (deep cycle and starting) that will turn over an eight cyl. engine.  The control switches have a series parallel switch that will help start the engine using both batteries in an emergency.  There is a switch for each of the batteries.  On most vehicles you wire the dual charging system using the output of the charging system so the START battery switch must remain ON.  The Aux. / House battery power can control all your accessories with the House Battery Switch.  The dual battery charging system runs about $150 on line the Odessey PC-680 runs about $110 delivered.  I photocopied the instructions and laminated them to keep a copy in the battery box JUST in case.

I am an experienced electrician so the design and installation work wasn't to bad.  The average guy could have a difficult time making a system like this work.  The box is mounted to the floor of my scooters (have 3 of the same scooter which have  400 watt alternators in it's 250 c.c. engine.)