dual battery conversion

Hi David (@rush-rentals), There are a couple of way to do this.  The way the factory does the 24 V system is that they add a second battery in the side pod and that is just used for starting the engine.  The car uses the rear battery to run the 12 V system in the car like the dash, etc..  The rear battery is charged by the engine electrical system.  The battery in the side pod uses a stand alone charger that is powered by the 12V system to for charging.

I have seen some people modify 12V (single battery) cars by adding a second battery in the side pod, or sometimes they put it in the passenger foot well.  For charging the second battery sometimes people use the Radical sourced charger and sometimes they just add a charging port to use a standard battery charger after the days racing is done.  The starter battery tends to have enough charge to do a weekends worth of starts without charging.

Here is a picture showing a simplified wiring diagram showing the single battery installation.

See the nest post for more information.

Here is a simplified wiring diagram showing the additional battery installation excluding the charging harness.  This would be the simplest installation, but you need to also add a charging port to charge the second battery because it will not get charged by the engine charging system.

See Next post for more information

Here is a simplified wiring diagram showing the additional battery installation excluding the charging harness.  This would be the simplest installation, but you need to also add a charging port to charge the second battery because it will not get charged by the engine charging system.

See Next post for more information

Here is a simplified wiring diagram showing the charger system installation

See Next post for more information

Here is a picture of the On-board Charger that Radical uses (The silver box).

Here is a picture of the sidepod battery installation in an SR3 RS (Gen 2 car).

a friend from the radical page on FB said he did a 2nd battery and does the charging of it after his weekend at the track. my worry with that is not being a deep cycle battery from running them down and then recharging will it last as long as being charged from the cars charging system? 

I do like that option as it seams like an easy solution . 

I did my own.  I used an Odyssey extreme battery and put it in the passenger footwell.  I made a foot bar to protect it so anyone in the passenger seat can’t kick it.  I put it in this location because it is far easier to get to it for maintenance etc…

I used the attached diagram and then added a contactor to run the positive cable from the second battery through and on to the starter and had it controlled by the safety switch so that if someone throws the safety switch, it truly kills power to everything.

i ran a charger line out to the passenger side air inlet same as the main battery hookup on the driver side.  It rarely needs charging, but is simple and easy to get to and hookup.

I had a lot of charging issues early on until I bought an AGM charger and used it instead of battery tenders.

@jking85 and Charley this info is fantastic thank you so much

Hi I have same starting problem under 12v. I want to make 24v system too with 2 battery connected but I have a question:

During starting phase do we have a risk of damage of the ecus with a 24v polution into the system or we can only have 24v in the starter ? maybe we could use a diode to have no return 24v in the wires ?

I have found this too, maybe it would be enough to boOst the starter ?

thanks

@nico-fr-18 

The second battery is on de-energized side of the start contactor.  12volts through the starter contactor to the second battery.  You won’t get the bump to 24volts until your on the backside of the second battery.  

the only thing I did was to add in an extra relay tied to the safety switch on the dash so in the case of a problem, throwing the safety switch cuts the circuit from the second battery to the starter.  I have been running this setup for 5 years, never a problem.

@jking85 thanks for your reply I will follow your wiring.

Kind regards 

Nicolas 

what amp power you suggest for the second battery ? the main battery is an Odyssey AGM 34Ah.

Ad as I will ad a vac robotic pneumatic gear shift would you connect the compressor to the firts or second (slave) battery ?

regards

nico

I use the attached.  It was in my car when I bought it as the main battery.  I went out and bought the original style AGM battery and put this in as the second battery.  When the really big expensive battery failed I went back to 1 of these as the main and start battery.  No problems since.  I did require me making a spacer for the original battery location as it is definitely smaller.