question

Your truck has a single 105ah agm battery for starting and auxiliary stuff?

Inconceivable!

Recently discussed with lots of detail, especially if you follow the link provided by wildebus. See

https://community.victronenergy.com/questions/119423/mix-agm-and-lifep04.html

Well I ordered all the parts today so will know soon if works as intended. I went with the Smart Battery Protect instead of the second DC/DC charger, saved about $200

OK battery pack is assembled and ready to put in the car :D

My last question is where to input the solar? I currently have a "dumb" MPPT regulator which is fixed on an AGM charge profile (often sits on 14.4v output in full sun). Panel only comes out when we are stopped and engine off.

If I wire it to the lithium and it's at 100% SOC, I'm worried the 14.4v will overcharge and damage the battery. Although I guess the BMS will disconnect to stop this?

If I wire it to the AGM (which is more convenient), I could have 14.4v on the "out" side of the Victron Smart Battery Protect and 13.8v on the "in" side. Will this cause current to flow backwards through the SBP and damage it?

Well I've had the hybrid battery setup running for a while now and it's working nicely.

Turns out the Victron Smart Battery Protect is a bit of a POS and doesn't actually fully isolate the battery in "off" mode. There was always a few volts still registering at the output and upsetting my careful plan.

I also decided that I liked the idea of a DC-DC charger from the lithium back to the AGM as it would maintain 100% SOC on the AGM all the way up until the Li was empty. Basically the main battery would always be on trickle charge while the car isn't being driven. Would be ideal to power my camping accessories and also maintain the AGM battery in between trips.
Didn't have room for another charger but I noticed that the settings in the Orion were not too dissimilar for AGM and LiFePO4 chemistries. Seemed redundant to have 2 identical chargers with near identical settings that never ran at the same time so I set about using the one Orion to charge either battery depending whether the engine is running or not.

I used 3 x 60 amp changeover relays and an Arduino to achieve this.
When the engine is off (no oil pressure), relay 1 NC connects the charger input to the LiPO and relay 2 NC connects the charger output to the AGM. Relay 3 NC connects the charger ground.
When the oil pressure switch goes high, the Arduino first drops out the remote input to the charger, disabling charge. There's a 4 second delay until it fires relay 3, dropping the ground from the charger and fully de-powering it. Another 4 second delay and it fires relay 1 & 2, connecting the charger input to the AGM/Alternator and the output to the LiPO. Another 1 second delay and it drops out relay 3 to reconnect the ground. Another 1 second and it connects the charger remote to begin charging.
When the engine turns off again the same thing happens but we end up in a low power state with no relay coils energised.

Here are my charge settings in the Orion. Its main job is to fully charge the LiPO, and maintain a full state in the AGM. It should never really have to charge a flat AGM so the bias is more towards charging the LiPO.
Absorption voltage: 14.2v
Float voltage: 13.5v
Bulk time limit: 10 hours
Re-bulk voltage offset: 0.1v
Adaptive absorption time
Maximum absorption time: 2 hours
Input voltage lock-out 12.4v-12.8v
I'm open to any input on tweaking these settings for a best compromise between the 2 chemistries.

And here are some pics of the battery build and and install under the driver's seat. Things are packed in tight! The space used was freed up by removing the obsolete 2000's era factory navigation DVD setup and telephone module. Not an inch of wasted space in these cars!