Dual Battery Basics

[pawleyk]

Hello all,

I've been researching dual battery setups, but I'm still unclear as to what I actually need. It seems that most articles and write-ups are discussing the intricacies of various isolators/separators/relays.

My question is- Do I actually need any of those for my particular setup? Why not simply wire the batteries in parallel?

I've got a 2005 silverado HD 6.0L gas. It's the very basic work truck edition, rubber floors, cranker windows, etc. No fancy electronics or crazy stereo systems. The under-hood battery(ies) will only be responsible for the standard starting and truck accessories, plus the very occasional winching duties, a 12v onboard air system, and possibly a small inverter in the cab to charge a tablet or two while on the road.

I really only want the dual battery setup for the increased capacity and the added peach of mind that comes with redundancy. Most of the discussions I've come across basically treat the second battery as a "house" battery, which I'm not sure I really need in this case.

The plan is to put a FWC on the back in the next couple months (ordering it tomorrow.. ) which will obviously connected, but isolated, from the starting batteries. The camper will have solar and it would be nice to have a system that charges both directions to keep the truck batts topped off during longer, sun-filled stops.

I'm only throwing the future camper plans in to give some context to expansion plans, but I'm really just trying to figure out what to do with the truck batteries in the meantime.

 

[Ducky's Dad]

If your truck has the extra battery tray in front (my K1500 Vortec came with an extra tray, apparently because they used the same body for diesels in that era), the easiest solution would be to stick another battery in there that matches your primary battery, and connect them with something like a Blue Sea Systems rotary switch. Use the switch to isolate them when you aren't using or charging the second battery. You just have to remember to rotate the switch to keep the battery charged. If you don't isolate the batteries from each other, they will drain simultaneously and then you have essentially no backup battery.

The next easiest thing is to use a switched solenoid isolator, like the one from Painless Performance. I have had them in two trucks for 17 and ten years, respectively, and they have been trouble-free. More expensive than a simple switch, but I can control the batteries from the dashboard, very convenient. And when the ignition is off, the batteries are isolated by default, so eliminates the possibility of parasitic drain on the backup battery. Some guys like automatic sensing/switching relays but I tend to avoid that kind of stuff.

 

[Korben]

Simply connecting them in parallel will work, many many diesels are set up that way factory and it works just fine for the most part. It has it's issues though, two batteries connected in parallel will tend to drain each other as they each have there internal voltage variations. This is made worse by dissimilar batteries and low resistance batteries like many AGMs. So if you want to only connect them in parallel then I suggest two new lead acid batteries. However if you have a good battery now bang for the buck your often better off installing an isolation gizmo or two to ensure better control and that they wont drain each other. The money saved by avoiding the purchase of second battery so they match can cover the cost of isolation items.
.
For what you have in mind there's two isolation items to consider. A battery charge isolator, these are your common 'house battery' isolators, they won't however allow the use of the second battery to provide starting power. Secondly a constant duty solenoid, wire it up to be on with ignition, as soon as you turn on your ignition both batteries are connected for starting charging, etc. The later sounds like your best answer to keep it simple and get more bang for the buck.
.
This can get complicated, many improvements can be made. But for now it sounds like a solenoid would be the way to go. I have a few of these used for that function and am satisfied with their performance http://www.amazon.com/PAC-PAC-500-500-Amp-Battery-Isolator/dp/B001YIPXR2

 

[rayra]

Not sure if the pickup has the same under-hood 2nd battery location as the Tahoe and Suburbans, it's up in the passenger corner by the hood hinge. I'm also not sure if that space is even tall enough to place a matching / same group-size battery.
For a simple parallel install the batteries should be the same type / capacity. A simple set of thick battery cables tying the 2nd battery to the primary will do the job. use the same gauge wire as the main cables on your primary, in this sort of install, as you'll be drawing the starting load from the secondary too.

The other option is a second same battery, but charged with an isolating circuit / diode, such that the 2nd battery is always charged but not tied to / used by the factory systems. You add all your add-on circuits, 'house' needs etc to it. But wire it also with a fat supply cable and a manual disconnect / rotary switch so it can be used in case of a failure of your primary battery. Or just carry the tools to physically swap the batteries.
The battery in back, the 'house', a true 'aux' doesn't matter if it matches, but I think it's a good idea so you can make a swap if necessary. For yourself or someone else in a pinch. Otherwise use whatever compact or odd-shaped sealed 12v battery you want for an aux / house source.

we have a whole subforum for the power stuff, the theory and many solutions are all there in many topics
http://www.expeditionportal.com/forum/forums/48-Power-Systems-12v-Solar-Gen

 

[smlobx]

I am not too familiar with GM products but I would look at what the diesel version of your truck has.

Also, don't overlook your alternator. In the case with Ford, the alternator in my diesel is only 110 amps which is what they put in the fusion...I upgraded to a 185 amp unit and my batteries are much happier now.

 

[Ducky's Dad]

I am not too familiar with GM products but I would look at what the diesel version of your truck has.

Also, don't overlook your alternator. In the case with Ford, the alternator in my diesel is only 110 amps which is what they put in the fusion...I upgraded to a 185 amp unit and my batteries are much happier now.

Some of the GM gassers already have the second battery box, empty. All you need is a hold-down and some cable to make a functional dual battery setup. My GMC came with a 105 amp factory alternator, and then I replaced it with a high-amp aftermarket alternator that failed and burned up my batteries and charging system in East BFE. Towed the truck to the nearest dealer and they installed another 105 amp factory alternator with a lifetime GM warranty. That was about thirteen years ago and that alternator is still happily feeding a dual battery setup with two Optima Yellow Grp 34s and a Painless solenoid isolator. Unless you are using something like an Odyssey 31M, the factory alternator is adequate for most uses. A bigger alternator is usually better, but not always necessary.

 

[mowerman]

My dual battery basics is basically very basic
2 batteries, main and auxiliary, the aux connected to the main via cable through an isolator switch. Charging of the aux commences via a 200 amp relay which is switched via the 12v output of the alternator, so the batteries are mechanically isolated until the truck is started, then they are both charging.
The isolator switch enables me to isolate them so I can jump start the truck from the aux battery.
Whole thing cost me about $30

 

[1stDeuce]

Lots of ways to do it, but I'll add another opinion/option...

I've not run isolators of any kind for a long time now on my dual battery setups. I've had no issues with one battery pulling the other down, even when they're not new at the same time, or even the same size, so long as they're both in good condition. The only downside is that if one battery develops a shorted cell, it WILL flatten both batteries. (Pretty rare if you take care of your batteries.) I've had Zero issues in 12+ years of running GM diesels with two parallel batteries.

I do have a "house" battery in my truck camper, but I wouldn't go that route again. It turns out I don't really need it after switching all the lights to LED and adding a solar panel. My recommendation is to just run a 10ga power wire back for the camper, and let it draw off the truck batteries, and let the solar charge them back up. That way there's one less battery to buy and maintain. You want big ga wire to keep the voltage drop low for the charge process. Use something significant to connect the camper too, like the 50A gray anderson connectors. If your camper has a 3-way fridge, this is almost a necessity anyway to get it proper voltage to work well on 12v mode while you're driving. If you use it that way, you must be ABSOLUTELY sure to turn it off of 12v mode when you stop though, as it will draw about 10A, and will flatten your batteries fast if you don't! (This is a old style 3-way fridge, not a new 12v compressor fridge...) If you have a compressor fridge, then it'll be happier with good voltage too. Note: the trailer wiring in most new trucks is NOT good for getting decent voltage to the camper...

The ONE group 31 battery in my camper rarely gets down to 80%, and only that low in the winter running the heater all night, and lights, laptop, tv, cell chargers, etc for hours in the evenings. Spreading the load between two group 27 batteries, or even two group 24's would result in each battery draining ~10%. No problem for any battery, and the less you drain them, the longer they live. My 85w panel charges the battery back to 95% before the sun even hits high noon most of the time, and only fails to charge to 100% on the cloudiest of days in the winter months, when the sun is low. With the camper running off the truck batteries, if you know that the sun isn't coming out strong that day, start the truck and let it run for 10 minutes in the morning to push the batteries up to 90-95%, and the solar will top them off from there. And put the biggest panel you can fit on the roof. I currently recommend the used Kyocera 120w panels that solarblvd is selling on their site and on ebay. The ones I have are still putting out over 95% of rated power, and they're pretty inexpensive and durable.

Hope that helps!
Chris

Good luck!
Chris

 

[oldnslow]

Your 4 Wheel Camper will have a battery in it (unless you get a shell model), that is your "house" battery. It will have an automatic isolator in the camper so it doesn't run your starter battery down. At least that is what they had about 10 years ago when I had one. You will be all set for that, no need to do anything.

I would not recommend running your camper off your starting battery as stated above. That will shorten your starting battery's life and may leave you stranded where you are camped, in the middle of nowhere. Starting batteries don't like to be discharged overnight like that.

If you add a solar panel (at least 80W) to your camper it will keep that battery charged up even when you are not using it. Every time you head out you will be leaving home with a full battery. That is nice. The solar won't charge your starting battery though. I don't think that is necessary unless you leave it parked for a month or more at a time. If you do that, you will likely need to replace the FWC-supplied isolator with a Blue Sea ACR or similar. I'm not sure what they are using now, but when I had one the isolator was a one-way unit. The truck would charge the camper but not the other way around.

 

[doug720]

"I've not run isolators of any kind for a long time now on my dual battery setups. I've had no issues with one battery pulling the other down, even when they're not new at the same time, or even the same size, so long as they're both in good condition. The only downside is that if one battery develops a shorted cell, it WILL flatten both batteries. (Pretty rare if you take care of your batteries.) I've had Zero issues in 12+ years of running GM diesels with two parallel batteries."

This is what I do also. Simple is good.

I change both batteries at the same time and both are the same model and make.

No issues at all.

 

[Ducky's Dad]

If you run dual batteries without an isolator, then you have doubled your capacity but you still have no backup in the event of failure. Seems that only solves half the problem.

 

[gatorgrizz27]

If you run dual batteries without an isolator, then you have doubled your capacity but you still have no backup in the event of failure. Seems that only solves half the problem.

Agreed. There are some great simple diagrams at the top of the electrical section. I'm going to install dual batteries with a 600 A constant duty solenoid which will automatically isolate and charge them, as well as allow for self jump starting. I want an "idiot-proof" setup where I can't either forget to charge a battery or end up running both of them down by leaving the lights on in the middle of the woods somewhere.

 

[pawleyk]

Thanks for all the suggestions guys, this really did help me narrow down my options.

My truck does have a location for the second battery from the factory, so I just ordered the GM part number for the tray and hold down..

After reading through everyone's experiences and suggestions, I'm leaning toward an "isolated parallel" system. I'll just wire the batteries in parallel with 2ga cable, then put serious constant duty relay between them wired to a 12v+ with ignition. That way a draw with the truck off will only drain one battery, but the system will function as a basic parallel setup for starting and charging.

-KP

 

[pawleyk]

Lots of ways to do it, but I'll add another opinion/option...

I've not run isolators of any kind for a long time now on my dual battery setups. I've had no issues with one battery pulling the other down, even when they're not new at the same time, or even the same size, so long as they're both in good condition. The only downside is that if one battery develops a shorted cell, it WILL flatten both batteries. (Pretty rare if you take care of your batteries.) I've had Zero issues in 12+ years of running GM diesels with two parallel batteries.

I do have a "house" battery in my truck camper, but I wouldn't go that route again. It turns out I don't really need it after switching all the lights to LED and adding a solar panel. My recommendation is to just run a 10ga power wire back for the camper, and let it draw off the truck batteries, and let the solar charge them back up. That way there's one less battery to buy and maintain. You want big ga wire to keep the voltage drop low for the charge process. Use something significant to connect the camper too, like the 50A gray anderson connectors. If your camper has a 3-way fridge, this is almost a necessity anyway to get it proper voltage to work well on 12v mode while you're driving. If you use it that way, you must be ABSOLUTELY sure to turn it off of 12v mode when you stop though, as it will draw about 10A, and will flatten your batteries fast if you don't! (This is a old style 3-way fridge, not a new 12v compressor fridge...) If you have a compressor fridge, then it'll be happier with good voltage too. Note: the trailer wiring in most new trucks is NOT good for getting decent voltage to the camper...

The ONE group 31 battery in my camper rarely gets down to 80%, and only that low in the winter running the heater all night, and lights, laptop, tv, cell chargers, etc for hours in the evenings. Spreading the load between two group 27 batteries, or even two group 24's would result in each battery draining ~10%. No problem for any battery, and the less you drain them, the longer they live. My 85w panel charges the battery back to 95% before the sun even hits high noon most of the time, and only fails to charge to 100% on the cloudiest of days in the winter months, when the sun is low. With the camper running off the truck batteries, if you know that the sun isn't coming out strong that day, start the truck and let it run for 10 minutes in the morning to push the batteries up to 90-95%, and the solar will top them off from there. And put the biggest panel you can fit on the roof. I currently recommend the used Kyocera 120w panels that solarblvd is selling on their site and on ebay. The ones I have are still putting out over 95% of rated power, and they're pretty inexpensive and durable.

Hope that helps!
Chris

Good luck!
Chris

Chris,

Thanks for the advice and recommendation on the solar panels! What charge controller are you using for your setup?

-KP

 

[1stDeuce]

I use Morningstar Sunsaver charge controllers on both my truck camper (SS-6L) and my "Home" (SS-20L). They work well with flooded and sealed batteries, are temp compensated, and have very good PWM charge strategy with Bulk/Absorbtion/float modes. Only downside is the controller isn't really waterproof, but that shouldn't be an issue if you mount it inside. (It is potted and sealed, just not ideal to be putting it out in the crud, IMO.)

I actually have a Bogart Trimeteric on our home system, and according to it, the Sunsaver is doing a GREAT job of bringing the batteries right back to 100% every day. I was going to get a bogart charge controller, but spending another $200 to replace my $60 Sunsaver seems foolish.

Both the SS-6 or 6L (Doesn't matter for our purposes) are pretty cheap on fleabay. And they're actually rated for the current they say, plus a 20% overage or something like that. The SS6 is rated at 6.5A, so will handle up to a 120w panel without issue. (Running PWM, my experience is that you're not likely to get much over 6A out of a 120W panel on the best of days...)