Dual Battery Setup Question?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Rooskey

Rooskey

Joined
Nov 4, 2010
Threads
17
Messages
124
I have an 81 toyota and I am considering running a dual battery setup. I use a redtop optima now for everything including the winch and lights. I would like to run a second battery for JUST my winch and lights. I have a ramsey 8000rep, piaa 520 atp w/ 100watt bulbs. I am wanting to run another set of lights as well with equal wattage and amp draw. My thoughts are to only hook up my winch and lights to a second yellowtop optima only. I would then run a second wire from the alternator charge post to the secondary battery. Battery one will run the truck as normal and all offroad equipment will run off the secondary battery. Has anyone tried this and will the alternator be able to charge both batteries with out any issues. Thanks for the help!!
 
I run a dual battery setup, with an upgraded 500 amp solenoid from 12voltguy.com

I also have had very bad luck with AGM batteries (both odyssey and optima red top) in my '85 & '86 mini. Both have lost cells within 6 months of use. Contrarily the batteries I have found to work very well, is the group 27 EverStart Marine Battery from WalMart (made by Johnson Controls). After 6 years, and many deep discharges, they still work like a champ.

Something that is important, is to match the capacity of a battery. This means its important to have 2 batteries which are the same age and size (ie: same battery).

Remember: a starting battery is good for high-amp, short duration discharges (aprox 10 sec). A deep cycle is good for long duration, low amp discharges. If you use either battery in the other system, you will drastically decrease their life.

Also: never let a battery get below 10 volts.

If you do run different batteries in your truck, I'd recommend isolating the systems with dual alternators or some kind of battery isolator. The first option is far better than the second.

FYI: Your Winch will pull up to 450 amps for 4 minutes, whereas your lights will pull 20 amps for 2-3 hours.
 
Last edited:
GRM said:
If you do run different batteries in your truck, I'd recommend isolating the systems with dual alternators or some kind of battery isolator. The first option is far better than the second.
Click to expand...

I have dual batteries, and they are both different from each other. I use a small Odyssey to run all non-factory accessories (CB, HAM, pillar gauges, alarm, fridge, dash outlets, bun warmers, ARB, backup light, etc). I use a standard RV isolator (diode).

My observation. If I have nothing running on the aux battery it will over charge. I have dual digital volt meters on the dash, mostly so I can watch the condition of the aux battery when I'm in the boonies (fridge running, engine not). I've seen volts on the starting battery at 14.3V or so with the engine running and over 15V on the aux. I now keep something running on the aux battery all the time. Usually just the CB which doesn't drop the volts much with the truck sitting. It also creates a demand on the aux battery to keep it from over charging.
 
pappy said:
I have dual batteries, and they are both different from each other. I use a small Odyssey to run all non-factory accessories (CB, HAM, pillar gauges, alarm, fridge, dash outlets, bun warmers, ARB, backup light, etc). I use a standard RV isolator (diode).

My observation. If I have nothing running on the aux battery it will over charge. I have dual digital volt meters on the dash, mostly so I can watch the condition of the aux battery when I'm in the boonies (fridge running, engine not). I've seen volts on the starting battery at 14.3V or so with the engine running and over 15V on the aux. I now keep something running on the aux battery all the time. Usually just the CB which doesn't drop the volts much with the truck sitting. It also creates a demand on the aux battery to keep it from over charging.
Click to expand...

Pappy, Looking at a dual battery set-up. Does your isolator allow combining batteries? For jump starting or heavy loads like winching?
 
I no longer have the dual battery. My setup did not allow for jumping because the second battery was very small.
 
Pappy - Do you have a picture of your mounting location? Been thinking about running a similar set up? If it's possible have a picture of the dual Volt meter in the dash?
 
Mounting location:

dualbattery 003.webp


Keep in mind that there are now slicker ways. Something like this is cheap, and gives you a pair of USB jacks. You can even get panels with 12V outlets. https://www.amazon.com/dp/B01M7V1ME1/_encoding=UTF8?tag=ihco-20

Only one of the meters is lit in this pic. These little things are also stupid money and will be replaced by one of the meter/USBs above.

dash 001.webp
 
Oh, and my dash has changed. I needed more 12V, plus I needed to move my rear window switches. Of course, one of those 12V outlets now has a dual USB (4.2A) plugged into it ... times and life changes and one must adapt.

IMGP0019.webp
 
Last edited:
Tab crashed and lost post I was writing.....augh.

I've decided on bluesea 200amp VSR for isolator. It can be manually combine batteries for jumpstarting and winching by a switch mounted in cabin. My Alt is 160amp. Will mount accessory battery in back of 4rnr.

Need to research a more on accessories wired directly to 2nd battery vrs on accessory battery side of VSR. As of now only difference I can tell is running wires. Since I plan to mount VSR to driverside of engine compartment and all power wiring is ran there, battery/AFM swap will be a bit easier.
 
The time of diode type isolators is long past. Their cracking voltage is a voltage drop that results in neither battery getting a full charge unless the alt's regulator can be and is tweaked to bump the output voltage enough to compensate.

Better is a Voltage Sensing Relay or Automatic Charge Relay. I stay away from "Expedition" type parts and use stuff intended for deep water marine use. The established mfg's in that field are BEP Marine and Blue Sea Systems. Victron is a new name in that field that some are having success with. They're too new to me to recommend. BEP's products appeal to me better than does Blue Sea System's products, but I don't think that you can go wrong with either.
These units sense a charge on one battery and will stay open until that battery has fully charged or some set time has passed, then they close to charge the second battery. This occurs in either direction. If the charge source is the alternator, then the starting battery gets fully charged first. If the charging source is solar connected to the aux. battery then it gets charged first. When the charging voltage stops they will open, disconnecting the batteries from each other.

My preference is to pair a VSR with a marine battery bank manual switch. I work in the high performance contactor industry and don't have a lot of faith in open air contactors for high amperage use. For a small contactor to be reliable at that ampacity it needs to be hermetically sealed and back-filled with an appropriate gas.
 
Rooskey said:
<snip>
I would then run a second wire from the alternator charge post to the secondary battery. Battery one will run the truck as normal and all offroad equipment will run off the secondary battery. Has anyone tried this and will the alternator be able to charge both batteries with out any issues. Thanks for the help!!
Click to expand...

▲This is the way Chevy did it from the factory back in the mid 70's until ???? for dual batteries and the batteries did not tie together. They used a constant duty solenoid that engaged the charging wire to the second battery from the alternator when the ignition was in the on position.
 
I don't know for sure that it was wired stock that way, but my '79 3/4t 4WD Surburban with the OEM dual battery option came to me with a long 6ga. cable that connected both battery + posts together. Routing and mounting looked OEM to me, but no idea for sure. No constant duty solenoid. Haven't ever seen one on a GM truck that was OEM, but I haven't seen every GM truck of that era either.

One thing that truck did teach me was with dual batteries that the ground cables need to be ON THE SAME BOLT. The minimal resistance from having one battery grounded on one side of the block and the other battery grounded on the other was enough to set up a destructive self-discharging mode that disappeared when I moved the non-OEM ground cables to the same bolt. Only cost me one set of batteries.
 
ntsqd said:
I don't know for sure that it was wired stock that way, but my '79 3/4t 4WD Surburban with the OEM dual battery option came to me with a long 6ga. cable that connected both battery + posts together. Routing and mounting looked OEM to me, but no idea for sure. No constant duty solenoid. Haven't ever seen one on a GM truck that was OEM, but I haven't seen every GM truck of that era either.

One thing that truck did teach me was with dual batteries that the ground cables need to be ON THE SAME BOLT. The minimal resistance from having one battery grounded on one side of the block and the other battery grounded on the other was enough to set up a destructive self-discharging mode that disappeared when I moved the non-OEM ground cables to the same bolt. Only cost me one set of batteries.
Click to expand...

I ordered my Chevy truck new in 1977 and description above is the way mine came brand new from the factory. :meh:
 
pappy said:
Mounting location:

View attachment 1630152

Keep in mind that there are now slicker ways. Something like this is cheap, and gives you a pair of USB jacks. You can even get panels with 12V outlets. https://www.amazon.com/dp/B01M7V1ME1/_encoding=UTF8?tag=ihco-20

Only one of the meters is lit in this pic. These little things are also stupid money and will be replaced by one of the meter/USBs above.

View attachment 1630154
Click to expand...
Pappy, did the second battery do any damage to the inner fender? Support it in any way? I'm thinking of putting a second battery in the same location.
 
Yep. It's all cracked up ... which is one of the reasons it's no longer there.
 
There's all kinds of room under a pick-up bed for a second battery. 4rnnrs are a bit more of a challenge.

Or go with LiOn's reclaimed from a wrecked Nissan Leaf or similar. Then they fit purt near anywhere.
 
ntsqd said:
There's all kinds of room under a pick-up bed for a second battery. 4rnnrs are a bit more of a challenge.

Or go with LiOn's reclaimed from a wrecked Nissan Leaf or similar. Then they fit purt near anywhere.
Click to expand...

Excuse the lack of knowledge but can you mix lead acid/agm with LiOn in a dual battery system?
 
muddpigg said:
Excuse the lack of knowledge but can you mix lead acid/agm with LiOn in a dual battery system?
Click to expand...
Funny, I thought the same thing.
 
It's not simple, but they can be mixed. LiON needs a special charger/controller to function and not catch things on fire etc. Alt's output voltage would need to be adjusted up, but that just gives you an opportunity to put a 4 or 5 stage MPPT charge controller on the L-A battery(ies).

I suspect that it would be simpler to convert both the starting and the 'house' battery banks to LiOn. All of the batteries out of a wrecked Leaf are probably enough to set up two battery banks.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom