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Dual battery tech in 2024

kf4zht

Red Skull Member
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Curious what the general opinions on dual battery setups in 2024 is.

Got a 96 K2500 Burb 7.4l. Previously had the second battery tray added, but the battery on that side doesn't fit, the other batt is dead (2.5v) and the wiring is.... special (pretty sure OEM doesn't route the starter wire through the passenger control arms. Right now the plan for this thing is the camping/family hauler, some towing, general purpose kickaround. Not planning on making it into a living space - I have my trailer with its own battery for that. I am planning on installing a winch I already have and some radio gear.

So as I see it there are a few ways to do this

2 Starter batts, completely tied. Easiest to do, gives double CCA, can have something left on prevent starting
1 starter and 1 deep cycle batt, completely tied. Again, easy. Can have some charge limits and stuff between the two
2 Starter batts with isolator - Added cost of isolator, would find one with a failover function
1 starter and 1 deep cycle with isolator

I'm about to buy batteries, so I need to get that part figured out. Right now I'm leaning toward just 2 starter batteries. If I want to add an isolator down the road its only 1 added cable.
 
If you re-wire correctly, don't have a parasitic draw, then two batteries in parallel is more than enough.
 
Do you want 24V or twice the amperage 12V ?

I have a wiring diagram for 24V
 
Thats easier but put a Heavy duty switch in place in line for easier / faster charging when needed.


My radio batteries have a DPDT switch to charge when needed without disconnecting anything ham radio deep cycle batteries not starting.



kf4zht said:
Dont want to deal with 24v, just parallel 12v
Click to expand...
 
On my HEMTT, I installed two battery’s. Each has a master selinoid to switch it on. I can start with either one or both. No isolator. When it’s on, it gets charged. (If the motor is running) I use the same system that we use in starting a duel engine helicopter. Start #1 engine on “odd” days, #2 on even days. Some times on a long trip I will switch the second battery on and the first off to charge both. I generally don’t run both on at the same time because I’ve heard that it’s bad for the stronger battery.
 
Its bad to charge both at the same time as an un balance can happen and one will be ruined.

Need battery isolators.
 
What are you using them for? What kind of loads?

I've had a couple varieties now.

1st: dual batteries tied together 100%

Simple, cheap. Generally need same type and this is where people want same age and brand. Runs the risk of full run down if you let it sit.

2nd: dual "start" batteries with isolator.

This is what I've got now on my pickup, because it is very cheap. Isolator that I'm using is a 300 anp solenoid triggered off the key [alternator]. Batteries are only tied together when engine is Running to keep them both charged. Main battery only runs the starter, fuse panel and all accessories are run off second battery.

3rd: start + deep cycle.

Typically you will always want an isolator of some sort between these two. The different charge and float and rest voltages will result in 1 feeding the other until its dead or very low. With an isolator, no big deal. I ran an "auto disconnect" for a while. The "smart" ones don't suffer the voltage drop of the ones that use diodes. The diode typically takes up too much and significantly reduces charge from the alternator. Problem with the smart, the deep cycle had higher voltage and thr smart would stay connected until deep cycle was at or near dead before cutting off. Sent a bunch of energy to be heat and go away from the start battery.

This is why I went to the solenoid instead of smart isolator

The only reason I got rid if my deep cycle and went to a start/sealed lead acid style was to handle the 1kw occasional load from my tailgate. Everything else was fine with the 50ah lifepo4. I never had issues charging off the alternator directly.

Smart isolator would work well if my second battery had a rest nearer the 12.8v, or whatever the cutoff voltage is.

I'm a fan of isolated start and deep cycle. If I ever run my second battery too low to trigger the 8 volts needed to start my truck, I've got another wire I can just plug in and use the starter battery to start the truck. I ran my second battery so low once that my blinkers wouldn't blink, still started just fine :laughing:

If adding a solar panel, I'd add it to the deep cycle side. If the start battery is only seeing the starter load and isn't exposed to potential parasitic drain from the fuse panel or anything else, it will stay topped up for a long time between uses.

Ultimately it depends on desired use
 
dual battery's of your choice with a solenoid triggered off the ign switch
mine is setup with a 3 way switch so I have on with ign,off if I want to remove the 2nd battery and emergency/jump start powered from the 2nd battery if I completely kill the main battery
 
20240506_070303.jpg



Left my headlights on all weekend :emb:

Unplugged the aux and plugged in the start battery, fired right up. Drove it to work on the main and it charged the aux the whole way. After worked, switched back to aux for all the things except the starter and it worked as it should :rasta:

Cheaper than a switch, just as easy
 
Thats called series twice the voltage

Parallel is twice the amperage

Below that is another one, whats the Voltage?


series-wiring-for-battery-banks.png


20240507_185135.png



Muckin_Slusher said:
Could you post the wiring diagram for 24V
Click to expand...
 
Last edited:
PAE said:
Thats called series twice the voltage

Parallel is twice the amperage

Below that is another one, whats the Voltage?


series-wiring-for-battery-banks.png


20240507_185135.png
Click to expand...
Bottom is series/parallel.

The system voltage is 8 times the battery voltage, so

2.2x8=17.6 volts if those are individual leadacid cells.
13.2x8=105.6 volts if those are 12 volt batteries
8.8x8=70.4 volts if those are 8 volt batteries
6.6x8=52.8 volts if those are 6 volt batteries

None of those totals are common so I have no idea where you got that diagram.
 
PAE said:
Its bad to charge both at the same time as an un balance can happen and one will be ruined.

Need battery isolators.
Click to expand...
“battery isolators don’t allow full voltage to the isolated batteries”
 
In that case a switching network would be tbe next best option.

I have a diagram that uses a DPDT switch somewhere, will look when time allows.



Thatg9659 said:
“battery isolators don’t allow full voltage to the isolated batteries”
Click to expand...
 
Last edited:
Its a solar storage setup so 6x8=48 series plus x2 parallel.

Btw where / how did you come up with those numbers, they aren't calculated in fractional volts.


Muckin_Slusher said:
Bottom is series/parallel.

The system voltage is 8 times the battery voltage, so

2.2x8=17.6 volts if those are individual leadacid cells.
13.2x8=105.6 volts if those are 12 volt batteries
8.8x8=70.4 volts if those are 8 volt batteries
6.6x8=52.8 volts if those are 6 volt batteries

None of those totals are common so I have no idea where you got that diagram.
Click to expand...
 
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CarterKraft said:
I've used this system on a gas 6.0 with great results.

Also used the Blue Sea VSR's on boats.
Click to expand...

BIC-95300B install.jpg


I have a hellroaring as well, the BIC-20400B backup isolator. This keeps one battery as a spare, that gets charged but never drawn from unless you throw them together in parallel mode (in case of main battery failure or when winching). All loads normally only pull from the primary.

The only thing I don't like about it is the mounts for the lugs are very close together and necessitate using smaller lugs, which they provide. The small lugs don't fit on 2 gauge or larger wiring though, so the backup' battery leads have to be 4 gauge going into it, or cut down to fit into the smaller lug. I ran a short 4 gauge cable for 6 inches that attaches to mega fuse and then 2 gauge from the other side of the fuse to the backup battery.

A full size lug that fits on a 2 gauge output (to main battery in the pic) fits fine though. You also have to secure the lugs very well, because if they wiggle too much they are close enough that they will contact each other. You cannot crank them down, since it goes into a mosfet and has a low torque spec. I used jamb nuts with thread locker on the jambs nuts only. I put the jambs over the top to make sure the nuts don't back out and the cables stay put. Then I added a rubber boot over the center mounted lug so the other two surrounding lugs are less likely to make contact with it if they ever do get loose.

It is probably overkill, but I ran two separate negative cables from each battery to a main ground point and two separate positive cables from the hellroaring and the primary battery to a distribution block rated for 500 amps. The starter, winch, alternator and off-road accessories connect to the distribution block and main vehicle fuse box connects to the main battery directly at the battery post. The dual cables allow for more capacity and less voltage drop when tied together for winching and let you start the engine without getting out of the vehicle if just one of the cables becomes loose/corroded.

If and when the lithium batteries get cheaper and become better tested, I will see what it takes to run one or two of those. I am not onboard with the costs and the performance of them in the cold. Nor am I convinced that they are happy with being charged by dumber stock alternators, despite manufacturer claims.
 
As long as the lithium is tied in to a lead acid battery, a dumb alternator will charge fine. The excess will just be bled off as heat to the lead acid
 
Muckin_Slusher said:
Where did you get this knowledge?
Click to expand...
I ran a lithium iron phosphate secondary battery parralledlled with a sealed lead acid and charged by a dumb battery.

Only time I tripped the LiFePO4 internal BMS was when I overloaded it on the draw, had no degradation issues with it charging and maintaining itself, no issues with overheating or anything of the like.

I got rid of it due to the significant potential for damage when charging below 32*F and that a 1kw draw (liftgate) representing a 2C draw would trip the BMS.

mostly annoyed that the BMS wouldn't tolerate a 2C draw, that doesn't seem like too big of an ask when high draw tolerance is supposed to be a feature of lithium based batteries.
 
this is also assuming that whoever is using an off the shelf battery and not building their own and sourcing their own cells. even the cheapest chinese imports have built in BMS, the most basic of which only limit over charge. The fancy ones do a bunch more, monitor temperature and such.

the "problem" with a dumb alternator is that it won't stop producing even low current when there is little to no demand. Smart alternators will shut off and not produce when there is no demand, or however they want to maximize fuel economy by allowing some demand to be ran by the battery so the alternator can cycle load from time to time.

A lithium battery can't (shouldn't) tolerate a constant charge. By having it couple to a lead acid battery, there is always a load to suck up that extra charge from the alternator. Lead acid doesn't care if it gets a constant charge, it'll just continue chugging along.
 
In my experience, people often lean towards simplicity and reliability, which is why two starter batteries might be the way to go initially. You can always upgrade with an isolator later, as you mentioned, with just one added cable. It is also important to exclude parasitic draw.
 
AndyPatrick said:
In my experience, people often lean towards simplicity and reliability, which is why two starter batteries might be the way to go initially. You can always upgrade with an isolator later, as you mentioned, with just one added cable. It is also important to exclude parasitic draw.
Click to expand...
That's what I did. 2 starters and fixed the cabling. I can add an isolator with one more cable and I'm just as likely to add a lithium pack in the back if I ever need a house battery
 
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