Update on my attempted install today on the P400 5 seater: unfortunately, the Renogy 100 Ah Bluetooth battery is significantly taller than the standard (8.7” vs 7.9”) I did not catch this, and I found out it does not fit in the bottom left corner where others have made it work. I tried looking at installing horizontally, but it doesn’t really make sense.

@Guapo When you said you moved the silver mounting bracket, was there a trick to it? Mine is bolted along with the compressor, and it seems like quite a bit of unbolting of the compressor would be required.

 

Thank you! One more question while I'm at it: in the battery compartment, it looks like there is a more accessible positive lead next to the negative. Did you connect there, or directly at the battery?

 

Here is my progress report:I was able to loosen a bunch of bolts around the compressor to lift up that bracket and fit in my Renogy 100 Ah Bluetooth battery on a small plywood platform. I have secured it with straps to the standoffs in the floor.

Challenges encountered:
- Unable to bolt wood directly to floor - not enough clearance to fit a bolt into the standoffs and have any material leftover. Am using lashing straps directly into the standoffs, bolted, and around. I will put grommets into the straps so they don't wear apart.

I ran the wire from the battery compartment to the load space using the tips posted here. It was a pain to get it to route but I was able to do it eventually.

Challenges encountered:
- Removing the foam piece from the rear seats - one of the bolts was misaligned and cross threaded from the factory
- Got my fishing line stuck. Ended up removing the entire top of the rear seats to free it which is a ton of bolts and clips.



Rear seat with full top removed. You should only have to remove the foam piece, not the entire top!

Battery mount in bottom left of cargo area. Note: I did not end up lashing through the plastic in the end.

Wire fed into battery compartment. Still need to attach an inline MIDI fuse here.

 

Saw a guy on YouTube, down-under, installing a dual battery system in a 2022 D110 MHEV (he says a P300 but I don't think they make those in MHEV. Everything looks just like my 2022 P400 MHEV and he taped into a positive terminal found in the rear under-cargo space that he claims is coming directly from the starter battery ( pictured below). Can anyone confirm?

He says is his follow up comments that it has been running his system perfectly for the last few months, and power to that point shuts off with the car. That would obviously mean that the cable isn't a direct connection to the starter battery and must go through some relay. Wondering if a 40A DC DC charger would pull too much through that "mysterious" but promising circuit. It Would be a lot easier than running under the floor to the battery…

Also, anyone located a nearby ignition source? I don’t want to tap into the cigarette lighter plug under my air compressor, so as to avoid interfering with air compressor function.

 

@GrouseK9 looks correct (I was an electrical contractor).

It's limited to 12 amps (16 amp fuse) but this makes it really easy to tap constant and switched power in the rear.

https://www.powerfuluk.com/vehicles/...nder-l663.html

 

So you're referring to this possibly empty "power towbar" loom as being a good source of 12v ignition power. If I have a North American tow package with power-plug for trailer, is this loom in use?

 

For an ignition source, I think it's simpler to tap into the rear fuse box using a Micro II Fuse add a circuit which others have posted about. I don't believe there are any true "engine on" sources, so you will need to be careful not to drain your starter battery in accessory mode.

 

I would have to assume so.

 

@Guapo After all these months, have you noticed any excessive heat build-up under your cargo floor deck, when all your setup is hard at work?

 

So as I continue on my quest to a dual battery setup, I've been tinkering to learn more about the 48v MHEV battery setup... In hopes that the 12v connection in the under-cargo space will offer an acceptable "hot wire" instead of having to tunnel under the floor to get to the main battery (as a few brave and motivated souls have done here, kudos!).

Looking through my workshop manual, I found out that there's a DC to DC converter/charger in all that underfloor mess and this is what it says:

"The DC/DC is supplied with power from the MHEV battery. The DC/DC converts the MHEV battery voltage from approximately 48V DC to the 12V DC for the following:
All the vehicles 12V systems. The startup battery.
The output from the DC/DC charges the startup battery and provides all the electrical power for all the 12V components. The output from the DC/DC is approximately 14V.
The DC/DC supplies all the power for the startup battery. The DC/DC power for all the vehicle 12V systems in all Power Modes except in Power Mode 0 (vehicle locked and armed)."

Many of you may have known this already, but I had assumed that the power flowed the other way. So with this information, it seems that the alternator must charge the 48V battery and then it's voltage is converted to 12v by the DC DC charger and sent on to the main starter battery and all the 12v systems. Leading me to believe that the current coming out of the DC DC charger must be the same as the starter battery. Therefore plugging in to the large (4ga) cable coming out of the DC DC charger should be safe since its nearly the same as plugging into the starter battery itself. I would obviously put a 80-100amp ANL fuse between this connection point and my own DC DC Charger (which I don't think I'll go any larger than a 40amp Renogy or similar and I'll be sure to protect it with the built in limiter). And since there seems to be current coming from this point up until you lock the doors, I'll be sure to include an ignition source to shut down my DC DC when appropriate.

I did some voltage tests with the car in various conditions that I'll show below along with my understanding of the voodoo electronics: