Dual Battery: not rocket science?

[MOAK]

Hello all.
I have done a lot of reading up on dual battery systems lately and since we now have a fridge freezer, I'll be installing mine this month after I get all my parts together... First off I'm using AGM batteries, 34R, 750 cold cranking amps, and 55 amp hours, perfectly paired in our 80. All my research has led me to one conclusion, Keep It Simple... I drive a Freightliner (18 wheeler) and it has two sets of 4 each AGM batteries. the 1st pack is used for starting and maintaining operations of the drivetrain and essential components of the tractor just like any automobile. The 2nd pack is used specifically to operate climate control, accessory lighting, and accessory power to the bunk while the rest of the truck is shut down,, In the expedition world we do things a bit different as we source all power from the operational battery and the second battery is simply a back up in case battery #1 should be drained while camped overnight. After speaking to several mechanics I have come away with a few things in relation to how I will install my dual battery set up. The ground from battery #2 can be run to the chassis of the vehicle, no need to ground it to battery #1. (The two battery packs in the Freightliner are not grounded to one another).. A battery monitoring system with all the bells and whistles is not necessary.(not in the Freightliner either) The stock dash gage tells you if things are charging or not... A manual switch to isolate and prevent battery #2 from draining is all that is necessary. (shame on me if I forget to pop the hood and flip a switch) One only needs to turn the switch,, on while driving, and off at camp. (the Freightliner has an auto solenoid switch for this and it has failed on two occasions and drained both packs down) I know, I know, this is an old school way of running two batteries, but really, is there anything wrong with tried and tested and reliable old school? I'm interested in all your thoughts... but throw something new at me that I haven't heard before. Thanks all !!

 

[IdahoXJ]

What are your thoughts on one of the batteries being a deep cycle? I have been wanting to do a dual battery system and your "keep-it-simple" approach is of interest to me. I may have to locate one of my batteries in the rear of my XJ because of limited room under the hood. I will be watching this thread. Thanks.

 

[Martyn]

Deka Intimidator is a marine battery designed to be a starter/ deep cycle battery. Very good choice for this application.

IBS offers a simple solution for what you are looking for. A smart relay with no monitor that manages a dual battery set up. It is designed for use in law enforcement and EMT vehicles. The relay is small and just has a red and green LED display on it. Contact George at Extreme Outback for more info. He doesn't have this part on his website as he usually sells it direct to police departments and ambulance services.

I'll post more info on it if I can dig it up.

 

[MOAK]

What are your thoughts on one of the batteries being a deep cycle? I have been wanting to do a dual battery system and your "keep-it-simple" approach is of interest to me. I may have to locate one of my batteries in the rear of my XJ because of limited room under the hood. I will be watching this thread. Thanks.

Well now, the battery system is installed and we went on our first journey back in July. A 6500 mile round trip out to the Cascade Range in Washington St. The dual battery "manual" system performed flawlessly, as opening the hood every evening to check fluids and turn the switch to "off" was very easy to remember. Popping the hood in the AM and turning the switch to "on", was as routine as performing my Pre trip and post trip inspections that I have been doing for over 35 years and that all of us should be doing with our personal vehicles on a routine basis. Being overlanders, I assume that all of us are a bit a--- retentive when it comes to pre and post trip daily inspections. To answer your question, the batteries I am using are deep cycle AGMs.. The batteries must match, and be of the same age in order to ensure longevity of them. If you mis-match one battery will draw down quicker than the other, and be a burden to the system, hence, premature wear. good luck...

 

[colierar]

I just installed this on my old Chevy to feed the camper with a deep cycle battery. My batteries do not match. I run one deep cycle and one regular starting battery. I love this thing. Easy to install and never have to mess with it. It basically makes the start battery a priority and charges the deep cycle as needed.

http://www.amazon.com/dp/B004QCDE9M/ref=sr_ph?ie=UTF8&qid=1412525660&sr=1&keywords=battery+isolator

 

[dwh]

The batteries must match, and be of the same age in order to ensure longevity of them.

In the system you have described, this is not accurate.

Batteries must match - same type, age, size, equal wiring, etc. when they are tied into a full-time bank, but when they are only tied during charging, that is not a requirement.

The only thing that matters when charging, is that they both specify roughly the same charging voltages. And all 12v lead-acid batteries except gel type do specify roughly the same charging voltages.

In other words, the charging system will hold the "12v bus" at a certain voltage - on my truck it's 14.5v - and each battery will suck (well, suck for a few minutes, after that they basically just sip) however much juice it can at the moment depending on that battery's internal resistance, the wiring and the supply voltage of the bus.



Now I'll...um...examine...your example...

If you mis-match one battery will draw down quicker than the other, and be a burden to the system, hence, premature wear.

Pre-trip, you open the hood and flip the switch to tie the batteries. Post-trip you open the hood and flip the switch again to isolate the batteries from each other, and your second battery becomes just a backup to start the truck in case you draw down your primary battery too much.

Since the batteries are NOT tied while being drained, and only one is actually being drained, a mis-match doesn't matter. The second battery cannot be a "burden to the system" - it's not connected to the system (or as I would say, "the bus").

As you say, one battery will draw down quicker than the other. Well, yea...especially the way you're using yours - where only one is being drawn down anyway.

So you're not going to get equal longevity even if you have a matched set - the battery that is actually being used will wear out, while the other battery, which does nothing except get a top-off charge whenever the truck is running will last forever.




Also, from your original post:

In the expedition world we do things a bit different as we source all power from the operational battery and the second battery is simply a back up in case battery #1 should be drained while camped overnight.

Hrmm. Dunno if you're using the "royal we" here, but that's not the way I do it, and I think probably not the way most people do it.

The way it's commonly done, is to do it the way your Big Rig is done - one battery for engine starting/chassis use, and the second battery to run aux loads. Then most people either use a manual switch as you do, or an automatic isolator (commonly solenoid type rather than diode type) as I do, to tie the batteries when the engine is running to charge them.

I use a starting battery for chassis use, and a deep cycle for aux loads. (In other words - the right tool for the job.) They are not the same size, age, type, manufacturer, etc. - and it doesn't matter. They both want to be charged to 14v+ and the truck's charging system does hold the electrical bus at 14.5v when engine RPM is above idle.

Since they are separated when the engine is off, it doesn't matter that they don't match and the deep cycle will certainly wear out faster, because it's doing all the work of supplying the aux loads while the engine is shut down. The chassis battery does nothing while the truck is parked.

I've worn out and replaced 3 deep cycle aux batteries in the (uh...can't remember offhand...6 years or so) since the last time I replaced the starting battery. Next time I replace the aux battery, I'll probably do both since the chassis battery is about due to be replaced anyway.



(And yes, 3 deep cycle batteries in 6 years is a lot of batteries, but I'm semi-retired and use my camper a lot. I also consider the house battery in MY camper to be disposable and so I just beat the unholy crap out of them by draining all the way, not always recharging ASAP and not always recharging them fully when I finally do get around to charging them. Basically, what every expert tells you not to do - I do regularly. I don't make a hobby or a career out of babying, nursing and nannying batteries. So personally I just buy cheap deep cycle batteries and hammer them into the ground and replace them regularly.

But, also consider that those 3 batteries cost a total of...I dunno...maybe 250 bucks. About the same price as buying one good AGM deep cycle and taking care of it to make it last while damn near full-time living in the truck. And even if I did spend the money and take the time to baby a good battery - would it last for 6 years of almost full-time use? Unlikely.

And I ALWAYS DO spend the money to get a good quality chassis/starting battery, because I want the truck to always start, and I'm not going to abuse that battery anyway.)

 

[colierar]

^^^ This, this is exactly the way to do it and the way I also put it to terms about the aux battery. Great write up.

 

[guts]

Well it looks like someone already beat me to correcting you about "how most overlanders" do it; however I have been looking around at different ways to set up an aux battery and someone brought up the idea of using golf cart batteries.... They are usually high AH deep cycle batteries. They are 6v so you would just wire them in series so they act like one 12v. then you would get something ridiculous like 500 or 600 AH out of the 12v set up. I'm just not really sure if it would still be safe charging this set up right off the main battery through a solenoid or whatever. Just a thought, maybe dwh will hammer me for this but that's ok

 

[dwh]

Well it looks like someone already beat me to correcting you about "how most overlanders" do it; however I have been looking around at different ways to set up an aux battery and someone brought up the idea of using golf cart batteries.... They are usually high AH deep cycle batteries. They are 6v so you would just wire them in series so they act like one 12v. then you would get something ridiculous like 500 or 600 AH out of the 12v set up. I'm just not really sure if it would still be safe charging this set up right off the main battery through a solenoid or whatever. Just a thought, maybe dwh will hammer me for this but that's ok

Nah, I only hammer people for telling others stuff that is wrong.

Trojan 6v T-105s are 225 amp*hours. Two in series to get 12v would be a 225ah string. Two strings in parallel would get you 450ah. It would be totally safe to charge them through a solenoid. But depending on how much you draw them down, vs. how much time you spend driving, you probably won't get them full.

Better bring along a small generator and a decent battery charger to make sure.

 

[CaliMobber]

Your right about them not fully being topped off with the alternator since most alternators only get 14.4ish and lead acid needs closer to 15v to get full

You Just need to have my setup and put solar panels on your roof and a morning star controller so the sun will top the excess power needed


I started with a manual solenoid but it ended up breaking and now they are just always tied together to make one big batt.

I think the best system out there is the blue sea marine automatic switch with a manual option. when the it sees like 13.5 it connects them and stays connected. when you turn off the car and voltage drops under like 12.7 for more than 30 sec it disconnects them. It also has a manual switch so if you are pulling a big load with like your inverter and it pulls the volts down they will stay connected.


My future plan when Funds allow and when my one of my optima's dies is to get one huge deep cycle for my fridge and accessories and keep a optima yellowtop for starting and use the blue sea to keep them connected.

 

[jatibb]

wire em like a dual battery system on a boat.Perko battery switch with built in isolator works great....select #1, or #2, or both. isolator lets you switch while running so as not to disconnect alternator in between selections

 

[dwh]

wire em like a dual battery system on a boat.Perko battery switch with built in isolator works great....select #1, or #2, or both. isolator lets you switch while running so as not to disconnect alternator in between selections

That's if it's a "make before break" switch. They also come in "break before make" so you gotta pay attention to which one you're buying.

 

[nixid]

DWH
What batteries do you use? I understand from your posts how you treat them.

(And yes, 3 deep cycle batteries in 6 years is a lot of batteries, but I'm semi-retired and use my camper a lot. I also consider the house battery in MY camper to be disposable and so I just beat the unholy crap out of them by draining all the way, not always recharging ASAP and not always recharging them fully when I finally do get around to charging them. Basically, what every expert tells you not to do - I do regularly. I don't make a hobby or a career out of babying, nursing and nannying batteries. So personally I just buy cheap deep cycle batteries and hammer them into the ground and replace them regularly.

But, also consider that those 3 batteries cost a total of...I dunno...maybe 250 bucks. About the same price as buying one good AGM deep cycle and taking care of it to make it last while damn near full-time living in the truck. And even if I did spend the money and take the time to baby a good battery - would it last for 6 years of almost full-time use? Unlikely.

 

[dwh]

Right now I'm running a group 31 flooded deep cycle I got at O'reilly. If I remember correctly the part number was 31DCM. They also had a 31DCMJ. The J is made by Johnson controls in Mexico, while the other is made in USA by East Penn. I paid a few bucks extra for the American made and had to wait a week for it to get delivered to the store.

Been around two years and it's due for replacement pretty soon.

Before that I had one from Autozone. Don't recall the details except it was a flooded group 31 @ 115ah.

 

[nixid]

If the house battery is going to be in the passenger compartment then it should be AGM due to the Hydrogen gas from charging?
And by " I just beat the unholy crap out of them by draining all the way," do you mean down to 0% or down to 50%?