Basically all you need to do is get a good battery switch, a second battery, and some wire that is the correct size. In the past I have used a switch made by Perko, it allows you to run on either battery or both plus it allows you to switch which battery is in use while the engine is running (it is a make before break switch). To install the switch you have to cut the end off the heavy gauge wire from the battery to the alternator (at the battery end) and connect it to the "load" lug on the 3 way switch, then run a battery cable from the + terminal on each battery and connect it to one of the "batt" lugs on the switch.
This is as far as I've got on my 2001 F150 Supercrew. I can't figure out whether I can #1 disrupt that wire coming up from that alternator -at the firewall, or #2 merely tap into it at the fire wall. Either way may cause the vehicle ignition system to be unhappy with me. I'll have to ask the dealer...which I hate talking to. You can see the thin alternator wire coming across the top of the dual batteries on its way to the ignition relay at the fire wall. You can also see the empty nut/screw on the blue isolator waiting for an alternator wire.
Is the box shown on the battery a dual battery adapter or an battery isolator, in either case get your docs from the manufacturer of that box. I have an isolator that has to be hooked up from the alternator, not the battery. It's wired in such a way that the alt always has a load on it.
you better be carefull with some of those switches like that i installed one on my boat one day to charge both batteries while the engine was running a stating batt and a trolling batt and ended up sending 24v to the system and melted every wire in the boat. and i followed the manufactures instructions for a 12v system but they were wrong or the swich was marked wrong its been years and i dont remember. i just remember being stranded in the middle of a bayou and pissed.
I am going to build a carputer (computer in a car, in place of my head unit(run my speakers off of it too) and I was thinking of having the system run off of the batteries but if I wanted to run it while the car was off I could run it off of one battery and not kill the starting battery so I could throw a bbq at the beach and not be stranded miles away from other cars
that is exactly my intention too. 2 batteries, 1 starting, 1 deep cycle, both always charging. when i want to i throw a switch, isolate the deep cycle and run the headunit while having no effect on my starting battery.
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