The Wrangler Northwest power products dual-battery relay and cable kit from quadratec allows the batteries to be connected in parallel. Connecting in parallel allows double the battery capacity (amp hours) for your vehicle while maintaining the charge in both batteries.
Dual batteries are a great aid to any vehicle, especially a 4x4 that uses multiple power-hungry devices such as a winch or air compressor. We had previously installed a Kilby dual-battery tray that housed dual Optima batteries in our '01 TJ but had neglected to install a proper battery isolation device. Through installation of the Wrangler Northwest Power Products relay and cable kit, we will be able to start the vehicle using the main battery, but once the engine is running, both batteries are joined for charge and discharge. Also, with the engine off, both batteries are isolated so accessories connected to the second battery won't drain the main battery.
The Wrangler Northwest cable and relay kit includes a 200-amp continuous-duty relay with silver alloy contacts that are said not to stick or corrode. The relay is weather-resistant and will also allow us to install an in-cab battery manager kit at a later time, should we elect to. The cables are made from super-flexible, fine-strand, high-amp copper and are labeled negative (black) and positive (red), and they have predetermined ends with ample length for most underhood installations. All of the cable ends are sealed and strengthened with heat-shrink tubing.
In addition to relay and wire kits, Wrangler Northwest Power Products manufactures a wide variety of single- and dual-battery mounting and wiring options. The company produces single and dual battery trays for most model Jeeps, in addition to battery manager and wiring kits and other items necessary for proper installation. Many of the Wrangler Northwest Power Products systems are available from Quadratec.
The dual-battery relay and wire kit includes a 200-amp continuous-duty relay and predetermined cables that are very flexible, making tight installations a breeze. We also ordered a set of marine-style terminals for the second battery. | 
An on-trail electrical issue had left our dual-battery arrangement lacking a few major components. The second battery had also lost most of its juice but came back to life after a night on the charger. | 
After removing most of the existing terminals, we installed the negative battery cable between the two negative battery posts. The vehicle ground, negative winch cable, and other accessory grounds were also secured to the negative battery posts of the main battery. |
We considered a few mounting locations for the relay but eventually found that the Kilby battery tray's hold-down would offer the easiest installation. After determining the proper mounting location, we attached it using self-tapping screws. | 
With the relay mounted, we installed the battery hold-down and made sure it didn't interfere with other components. | 
One of the positive cables was routed between the secondary battery and one of the posts on the relay. |
With the remaining positive cable installed, we covered the relay terminals with the included terminal boots. | | |