Battery relay/isolator clarification

[wew lad 5,000+ posts]

I'm going to run a dual battery set up, but the batteries are going to be different. Although their ratings are almost exactly the same (AGM, 55ah, 775cca) I still want to use a relay to separate the batteries from each other when my truck is off. I was looking at something like the NVX BIR500 or stingers 500 amp version, they're essentially the same.

Amazon.com: NVX BIR500 500 Amp Relay Isolator (BIR500): Automotive

Would I be correct to think that the isolator works by connecting both batteries in parallel (battery 1 is connected to alternator) when the vehicle is on via the 12v remote turn on. When the vehicle is off and the key is off the relay breaks the connection between battery 1 and battery 2. I need the supply current of both batteries when the vehicle is on, but I need them separate any time the truck is off. I'm not concerned about losing starting amperage from draining both batteries when the truck is initially turned on, my batteries never get low enough

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[adulbrich 5,000+ posts]

Just get a battery tender for the same price, that will be 10x more beneficial to prolonging the life of your batteries.

 

[wew lad 5,000+ posts]

lol I'm going to use a relay. don't need a float charger.

 

[adulbrich 5,000+ posts]

Then that is your mistake.

 

[wew lad 5,000+ posts]

It's not a mistake. Just because you don't agree about the way I'm going about this doesn't mean you need to steer my thread off track, PM me if you want to discuss it. If you have anything to add regarding the functionality of a battery relay then please, enlighten me.

 

[adulbrich 5,000+ posts]

All the relay does is separate your batteries when the car is off. They are discharging, just like they would if they were sitting in your garage or on a shelf. They aren't connected, and equalizing. There are still "internal battery losses", because a chemical reaction continues to happen inside the batteries. Float charging maintains a battery's cycle life.

Also, float charging reduces sulfation that occurs if a battery is not fully recharged. Also, your batteries will always be drained by your head unit and vehicle's electronics that need to save settings.

I'm sure @av83 can add to and/or correct my statements. He works at a battery shop.

Why are you so stuck on an isolator???

Do you see any big dogs using them?? No (only exception may be if they compete in a class that requires the vehicle to be turned off). You do see them using float chargers.

 

[av83 10+ year member]

I had a fvcking paragraph and then some written out when my terrible signal wiped it out upon sending. Anyways, long story short, I would take nice maintainer over an isolator in most cases. I just top mine off from time with a nice charger and i have an xs d3100 in back and an Exide 78 up front. You'll be fine.