We charge equipment continuously and most of our electronics demand power 24 hrs. a day. Heavy loads on a single battery isn't an option thus we opt for two batteries.
So there's a "starting" battery and a "house" battery. The "starting" battery is exactly that - power reserved for starting and running the truck and factory electronics. The "house" battery is essentially an accessory battery; everything aftermarket you'll install. With exception to the winch, our house battery will power the fridge, lifts, 3 full time USB and 12V outlets, communications and an air compressor.
I custom built my own dual battery install in the Tacoma last year with a Trail Gear Battery Cage. For the 4Runner, we opted for a kit. Its a bit tight under the hood of the 5th Gen and there obvious space for a second battery behind the passenger headlight but I wasn't willing to fab something with our Season 3 shoot closing in. At the time of purchase, the best option we could find was the dual battery kit from ShrockWorks.
ShorckWorks has a well thought out kit that reuses various parts an pieces that come with the truck. Everything is well documented in the instructions and to be honest, the hardest part of the install is separating factory harness plugs, ha! It does take a bit of time but again, it's well thought out and very clean.
Next, we connected the batteries with a DFNA Dual Battery Isolator Kit. There's some super pricey options out there and some very simple DIY solutions but the DFNA is the best of both worlds in my opinion. The DNFA Kit comes with your wires and isolator but you still need a fuse block and fuse panel. I rely on BlueSea for my fuse accessories since they have a solid reputation in the marine industry.
So here's the general setup - starting battery to isolator > isolator to house battery > house battery to fuse block > fuse block to fuse panel. Simple right?
The DNFA Smart Isolator allows two batteries to be charged at the same time. When the engine is started and the start battery reaches 13.3 volts, the engages, allowing two battery banks (start and house) to be charged simultaneously. When the voltage drops below 12.8 volts (i.e. the engine is stopped), the SBI disengages, separating the batteries. This system eliminates the possibility of draining the start battery and protects sensitive electronic equipment powered from the house battery from harmful engine start up spikes.
So there's no external power monitor with fancy LEDs and such but you can always install that if you feel like you need it. My general rule is, "there's power OR there's no power."
With everything setup in the 4Runner under the hood, we then routed all of the fun stuff through the firewall and even installed a second fuse panel underneath the rear seat for add-ons in the back. There's definitely room for adding more but we need some seat time in the 4Runner before we install a bunch of stuff we don't need.
Next up, the drawers...