running 2 batteries, pros and cons.

I just stumbled across this video of what i had in mind for my 98 tacoma, running 2 batteries, i have a lot of questions. Can anyone with this setup or something similar help me out, thanks.

https://www.youtube.com/watch?v=ja5sE_-ikdg

 

Don't have this system, but am planning a similar system, with the exception of a voltage sensing automatic relay. I have done dual battery systems before. Do you have a specific question(s)?

Biggest challenge is where to put the additional battery in a Tacoma. There is a spot, passenger side, close to the cowl, that is an option on Off Road and Pro models.

 

alright thanks for the reply, in the videos comments people are saying the accessory battery will drain the start battery if the charge is lower than the start battery, so how do you prevent that from happening ? would having an on off switch spliced in the wire that connects the solenoid to the 12v ignition be a good idea to start the car first and then allow some time to charge the accessory battery ?

 

I would start with determining if a bigger single battery would be enough for your needs, an extra battery adds a lot of weight and increased complication.

 

Have you seen this thread:
https://www.tacomaworld.com/threads...ts-see-them-multiple-batteries-thread.295653/

I got a setup from Off-Grid Engineering
https://www.tacomaworld.com/threads/off-grid-engineering-dual-battery-system-q-a.468553/

 

Disadvantages include weight, expense and added complexity.

So to me the first determination is if you really need it. If yes, do it well.

 

I've always wondered the use-case of 2 batteries. It seems to me that the only use would be for running accessories when the truck isn't running. If that's the case then the 2nd battery should be a deep-cycle battery with it's own charging system (since it's a little different than a starting battery's charging system). I wouldn't want any power coming off of the starting battery when the truck isn't running, especially in a camping situation. If you need more amperage when the truck is running then that's the job of a larger capacity alternator.

 

The use of the solenoid he has wired into the ignition is to prevent the drain of the starting battery when the ignition is off, at least in theory. The basis of this setup is to wire them together and when the vehicle is running and the alternator is charging the starter battery the accessory battery then "drains" or equalizes with the starter battery and thats how it charges. Then once the vehicle shuts off the solenoid closes and doesn't allow the accessory battery to drain from the starter. So to answer your questions. The point of the setup is to drain so you don't want to completely prevent it and the solenoid is the off switch to prevent the drain of the starter battery when the ignition is off.

 

The specific method in the video from your original post can work, but it has some weaknesses you should be aware of:

The video shows an ignition-on triggered solenoid. This leaves the batteries connected a LOT of the time. Mismatched batteries tend to push-pull each other when they are connected, which reduces their lifespan considerably. Ideally, this method would use batteries of the same group size, brand, AND production run to minimize this problem. Also, depending on the load your system requires, if the truck has the key on, but the motor off, you could run down both batteries.

The fuse method that is suggested does NOT protect between the batteries and the fuses, only the wiring between the two fuses is protected. If you had an accident, or by some other means accidentally shorted the wire between the battery and the fuse you could have a very big problem. It wouldn't cost a lot more to use MRBF fuse blocks to solve this problem.

The system described in the video only allows for 80 amps between the house and starting batteries. I assume that this is because the solenoid he is using is limited to 80 amps. A starter motor can pull a LOT more than 80 amps. Especially if it is cold. You may live in a warm climate, but in cold country this could be a problem. I usually design around a minimum of 200 amps. This will require bigger fuses, bigger wire, and a higher amp rated solenoid.

You can seriously reduce the push-pull problem and the problems associated with having different house and starting batteries with a voltage sensing, automatic charging relay, or eliminate them completely with a DC/DC charging system, but that will completely blow up your budget.

Incidentally, the video recommends 12 gauge wire for the ignition trigger to the solenoid, this is gross overkill. The recommendation is a strange anomaly in a system that is designed around strict budget concerns. 18 gauge would be plenty.

 

An on/off switch for the wire that connects the solenoid to the ignition is to prevent the start battery from equalizing with the aux battery seeing as the aux battery is going to be used for camping, so when the starter battery has started the engine flip the switch to connect both batteries and charge the aux battery. im assuming this would work but not 100 percent. let me know what you think.

 

You would probably want a separate voltage meter on the aux battery to confirm it is charged before you turned off the switch.

 

but do i make sense or am i missing something ? im going to try it out and post a vid/pics and see how it works.

 

Offgrid4x4 makes a jump starter kit for their dual battery system.

 

Yes, should work fine.

 

for sure thanks for your input.

 

I added a second battery about five years ago. I used to off-road solo a lot and got tired of lugging along a portable battery pack. Back then, the battery packs weighed as much as the car battery. Today, you can get a small lithium battery pack that is a quarter the weight. But, I still find them lacking in capacity.

My setup is on the affordable side. I have a DPDT in the cab to manually operate a

$83 Cole Hersee 24213 12V 200A Continuous Solenoid

Cole Hersee 24213 200-amp solenoid. The switch allows me to connect the aux battery to the car’s charging system at will, or run power to its own circuit via a second solenoid relay.

The simplest method of connecting an aux battery is to add an on/off switch between the aux battery and the primary/house battery. A switch like the Blue Sea M series models are rated to 900 amps intermittent, for cranking an engine. You need to be able to disconnect or ‘isolate’ the two batteries when you turn off the car so the weaker one does not drain the stronger one, or dissimilar one. Like my system as my aux battery is an AGM battery.

 

I gave solar panels a thought but that was too pricey for me right now. where would you splice the on off switch on the line ?
i was thinking of adding a killswitch on the 12v ignition connection that goes on the solenoid.

 

Where to wire the on/off switch depends how you wire the aux battery. Simplest wiring is to run positive to positive and add an inline fuse and the switch anywhere along the wiring. You could even run the wiring into the cab to place the switch there, but you would need to drill through the firewall. That’s where solenoid relays come into play; the solenoid sits between the two batteries and the solenoid is controlled by a switch or wired to the fuse box to connect the batteries when the ignition switch is powered up.

 

this is where I'm planning on putting the switch

 

That is the correct location. You do not need to use 12 gauge wire, 18 gauge is plenty.