Reddit reviews ONLINE LED STORE 12V DC 200 Amp Split Charge Relay Switch - 4 Terminal Relays for Truck Boat Marine

Is there any reason why you wouldn't just buy a normal 12v relay and run it to the ignition switch from the fuse panel instead of spending $60 on one with a relay built in? For example use these:

https://www.amazon.com/OLS-6-Way-Blade-Indicator-Protection/dp/B00QMTAZ1W/ref=sr_1_3?ie=UTF8&qid=1497658098&sr=8-3&keywords=fuse+panel

https://www.amazon.com/OLS-Split-Charge-Relay-Switch/dp/B01MYPTVJD/ref=sr_1_1?ie=UTF8&qid=1497658136&sr=8-1-spons&keywords=12v+relay&psc=1

Sort of. There's sort of a progression going on. It's a good idea to ensure you can cut the power between the two manually as a safeguard.

I used this
last time with a fuse on each battery, and just kept the accessories live to the house battery full-time. Turned it on when I wanted to charge or the odd case of boosting my starter battery from the house. Dead-simple hook up, I just had to pay attention to when I should have it on or not. Mostly cut it on before I start the vehicle, watch the dash voltmeter to know when everything's charged, then cut it off before I start using the house without the motor running.

I'm getting this one next time to replace the one above. I'll have the common on the accessories, and be able to run them off of the starter, the house, or both. "both" would also be used to charge the house off the alternator, and I'll have it there almost all the time, with the addition of a VSR (below). It also has an "off", in which nothing is connected to anything. You'd still want to wait until the engine is running to re-charge a dead house battery, and switch it to only "2" to keep from draining the starter battery, unless you install one of the next two items.

This makes a nice addition wired right alongside either switch. Tells you how much juice each battery has.

To keep everything 100% un-screw-up-able, this is going to go between my starter battery positive and my new manual isolator switch in back. If either side gets to charging voltage, it will connect to the other side. That means the alternator will always charge the starter battery, but also charge the house battery AND if I connect a charger to the house battery (like a generator or plugging in to shore; solar that fits on a van would take several days to charge a battery from dead to van-crankable), then it will automatically charge and maintain the starter battery, too. Neither can drain the other past the point it wouldn't crank the van.

Charging relays are much cheaper than a VSR, and are automatic in a more rudimentary way. This will do the job fine for most cases, and is a little less expensive than a VSR. The big lugs on it hook up just like the two on the VSR above, except it's not automatic - you hook the small poles up to stuff to tell it when to connect the big lugs. The small positive goes to the other, smaller wire going into the alternator, only allowing it to connect if the alternator is charging. The small negative can go straight to the large negative, but I'd run it through a small switch in the dashboard somewhere (and the other side of that switch back to the large negative lug) to allow me to disable charging house battery off the alternator. it's a decent blend of manual and automatic control, with a relatively tiny price tag. This pretty much needs to go under the hood, though, whereas the VSR could actually go in the power center or under the hood. Remember that either would go on the 4 gauge between starter battery and rear isolator, if present; it's the longest fat-wire in the whole system. some people skip the manual isolator switch altogether, and just go with a VSR or charging relay.

Only because I happen to have one of the first switches linked here already, I'd install it between the large lugs of the VSR or charging relay, to bypass it manually. If I didn't already have one, I'd just count on using a set of jumper cables to do that in the rare case I should need to turn that switch on.