Super Simple Dual Battery Project

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Rath

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Hey all, so a while back I decided I wanted a second battery in my truck, but I didn't need anything overly complicated, like solar charging, etc.

My plan was to keep it simple, and easy. Battery isolator between the main battery and a second battery to keep both batteries charged, but not allow my accessories to drain the main battery. I also wanted to run 12v power into the back of my truck to run things like lights, phone/camera chargers, etc. Eventually, I will be doing an inverter to run larger things like a fan, laptop charger, and have a place to plug in a powered cooler as well if needed.

As of right now, all I have is the second battery installed, and the 12V power run to the back. I will be updating this thread as the project progresses.


So for starters, I had to clean up some old terminals I had laying around. We always want to clean solid connections when dealing with electricity! So I cleaned up all the contact points on these terminals, and I had to re-thread them to a slightly smaller thread due to the threads being so warped and, well, I didn't have the proper sized nuts for them either. So I got started with that.











After that was all done, it came time to figure out battery mounting. I already had a storage box behind the driver's seat, which would work perfectly, but I needed a way to tie down the battery to keep it from sliding around inside the box. I stole some parts from an old battery relocation kit in my Rally car project and repurposed them to work. I chopped off the rusty nuts and welded on some large flat washers to act as an anchor against the bottom of the storage box, which allowed me to use the tie-down without drilling through the floor of my truck.









I will be upgrading to a deep cycle AGM, this was a temporary solution for a trip I had planned the day after I finished all this.




After that, it was simple, run cables to the back to my fuse block, and 12V panel!
I have a storage unit with lids beside my sleeping platform that I put all this in, so it wasn't visible unless the lid was opened. Clean and simple!







That's basically where it's currently at, I have some RGB lights installed, which are super nice as well.









Hopefully within the next couple days I will get started on the isolator and the rest of the wiring. I am just waiting on a couple of parts as I am also re-doing the positive cable from the alternator at the same time.
 

Rath

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Thanks! Was definitely super convenient being able to charge my cameras at the end of the day while I slept! being only USB 12V they weren't super fast to charge, but overnight did the trick! once I get an inverter and get full power to the back, things will be even better.
 
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Rath

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Thanks!


I should mention. The terminals are properly crimped. I just didn't have the proper size heat shrink for those ones, so I electrical taped them lol.

Wiring from main battery to isolator, to second battery is all 2 gauge I do have proper heat shrink for those. So those will be done, properly proper lol.
 
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Rath

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Small update to this, ended up stealing the battery I was using pictured above, to use as a starting battery in my truck, and purchased a proper Deep Cycle battery for use with the aux system. Much better off now.
 
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Hey @Rath - did you ever end up connecting your starting battery with the new deep cycle in back? If so, what did you use for an isolator? I've been mulling over options for years, though have two starting batteries for my diesel van (one under the hood and one on the driver's side frame rail).

What I've learned is that it is not wise to mix battery types (or even different ages or sizes of the same type) when charging both from the same alternator. Even when separated by a simple isolator when parked.

Different types of batteries have different charging profiles, and will accept a charge and discharge at different rates, causing one type to regularly overcharge (potentially dangerous) and the other to regularly undercharge when connected. It will eventually lead to premature failure of one or the other. Same is true with mixing differently aged, or differently sized, batteries of the same type.

Typical isolators combine both batteries into one big battery when connected and don't know there are different types of batteries involved. Mixing types, differently aged, or different sizes of the same type, is strongly discouraged.

Here's an article from Optima Batteries that explains things: Can I Connect Dissimilar Batteries In Parallel?

DC to DC chargers, however, have smart technology. They do not combine different types but sense which type has more charge (usually the starting battery) and lets it safely charge the other one (usually the house battery) through multi-stage charging. While it connects both types through it's smart circuitry, it does not combine them into one bigger battery, so protects both from over and under charging, letting them live longer.

It's what's kept me from adding a house battery to my starting system in the past though simple isolators or solenoids. Now that REDARC and CTEK have been perfecting great DC-DC chargers for years, it is far more possible to charge one type of battery from the other while running without hurting the other, or creating a potential danger. Renogy also has a DC-DC charger too, though I have no idea how well they work or how long they last. Both REDARC and CTEK have a proven history with DC-DC chargers and both are popular with off-road enthusiasts and adventurers around the world.

Here's a good vid that explains different types of popular isolators and DC-DC chargers. Listen closely and you will hear him explain that with "dumb" relays/solenoids used as isolators, you should not mix battery types, though DC-DC chargers are designed to do exactly that:


I suspect a lot of folks have combined different battery types with simple isolators and have prematurely aged or killed one of their batteries without knowing why. If you have a bunch of batteries around, maybe not a problem, though I would not want to do it, myself. A regularly overcharged battery is potentially dangerous.

Perhaps @REDARC_Ryan, who just joined OB recently and works with REDARC, will see this and chime in with his greater hands-on experience.


.
 
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MOAK

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Hey @Rath - did you ever end up connecting your starting battery with the new deep cycle in back? If so, what did you use for an isolator? I've been mulling over options for years, though have two starting batteries for my diesel van (one under the hood and one on the driver's side frame rail).

What I've learned is that it is not wise to mix battery types (or even different ages or sizes of the same type) when charging both from the same alternator. Even when separated by a simple isolator when parked.

Different types of batteries have different charging profiles, and will accept a charge and discharge at different rates, causing one type to regularly overcharge (potentially dangerous) and the other to regularly undercharge when connected It will eventually lead to premature failure of one or the other. Same is true with mixing differently aged, or differently sized, batteries of the same type.

Typical isolators combine both batteries into one big battery when connected and don't know there are different types of batteries involved. Mixing types, differently aged, or different sizes of the same type, is strongly discouraged.

Here's an article from Optima Batteries that explains things: Can I Connect Dissimilar Batteries In Parallel?

DC to DC chargers, however, have smart technology. They do not combine different types but sense which type has more charge (usually the starting battery) and lets it safely charge the other one (usually the house battery) through multi-stage charging. While it connects both types through it's smart circuitry, it does not combine them into one bigger battery, so protects both from over and under charging, letting them live longer.

It's what's kept me from adding a house battery to my starting system in the past though simple isolators or solenoids. Now that REDARC and CTEK have been perfecting great DC-DC chargers for years, it is far more possible to charge one type of battery from the other while running without hurting the other, or creating a potentially danger. Renogy also has a DC-DC charger too, though I have no idea how well they work or how long they last. Both REDARC and CTEK have a proven history with DC-DC chargers and both are popular with off-road and adventurers around the world.

Here's a good vid that explains different types of popular isolators and DC-DC chargers. Listen closely and you will hear him explain that with "dumb" relays/solenoids used as isolators, you should not mix battery types, though DC-DC chargers are designed to do exactly that:


I suspect a lot of folks have combined different battery types with simple isolators and have prematurely aged or killed one of their batteries without knowing why. If you have a bunch of batteries around, maybe not a problem, though I would not want to do it, myself. A regularly overcharged battery is potentially dangerous.

Perhaps @REDARC_Ryan, who just joined OB recently and works with REDARC, will see this and chime in with his greater hands-on experience.


.
That is the best explanation I’ve read concerning how a dc to dc charging system works.
 
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That is the best explanation I’ve read concerning how a dc to dc charging system works.
.
Thanks, @Moat. As I wander closer to being considered an old-timer all the time, I'm still able to retain and share at least some knowledge in a hopefully coherent fashion.

At other times I just babble endlessly.
.
 
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MOAK

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.
Thanks, @Moat. As I wander closer to being considered an old-timer all the time, I'm still able to retain and share at least some knowledge in a hopefully coherent fashion.

At other times I just babble endlessly.
.
Babble, ramble, excessive tangent taker; about the time I gather my thoughts they all want to run away again.
 
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Rath

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The isolator I have is voltage based, I believe it's 13.3v, once it sees that at the starting battery. It switches power to run into the second battery, once it sees it there, it isolates it back off again.

They're both the same brand, and type, only difference is ones a group 34 and ones a group 31 deep cycle, I don't see it being an issue at all, have seen many people run similar setups without issue.
 
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Rath

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Got everything wired up this weekend, I have a working 2 battery system now! Isolator works wonderfully. Although in the process I did discover I have a very small drain somewhere on my starting battery, which would explain why it was harder to start all winter after sitting for a few days... hmm. Going to have to try and figure that one out here.