I am about to go down the Lifepo4 path for my dual battery install. I have a DIY drawer system with a purpose built front cavity that houses my compressor/Fused distribution block/Lightbar digital drivers/ and will soon also house a 100a/h lifepo4 batt/BMS etc and Redarc DC-DC charger.
I have checked with the battery manufacturer and this particular lifepo4 setup is compatible with the Redarc DC-DC charger on the Gel settings. It will also be compatible to use as a jump start battery if the need arises, although to do this I will need to remove the battery and just connect jumper leads to the start battery. A bit of a pain, but shouldn't need to do it too often, if at all!
The battery and BMS c/w low ouput, high input voltage cut off Battery Control unit will set me back about $1000, yes it's expensive, but the main advantages are longevity if connected with suitable BMS and also weight. With a lifepo4 100a/h battery, this will give me the approximate equivalent of a 160a/h Lead acid battery due to the greater DOD of the lifepo4 vs the lead acid. The lifepo4 will weigh 15kgs, the equivalent lead acid is around 45kgs.
I'll be running my lightbars/compressor/fridges etc from the lifepo4 and with all on together, I'd be pulling about 80amps. The NW Pajero alternator is rated at 130amps, and will run comfortably at about 75% load, so say about 100amps.
Just to run the Pajero with the factory lights/air-con/ECU etc will draw a good proportion of this and not leave a lot in reserve for dual batts/spotties/etc etc. so my reasoning is to lessen the immediate load on the alternator and effectively limiting the additional current draw to 25 amps via a DC-DC charger.
I have been weighing this up for a while and can see advantages in both systems, the costs aren't so much different if you take into account using a quality lead acid + aux battery tray under the bonnet is going to set you back anywhere from $400-$800, particularly if you use an Optima etc. Most late model vehicles use a variable voltage and temp sensing alternator, some with ECU control via the canbus system, so really requires a DC-DC charger for optimum battery charging of the Aux. (There are arguments for and against DC-DC chargers)
The limiting factor with a lot of the lifepo4 batteries is the BMS, there are expensive models around that will not allow you to jump start if required due to the BMS they are using, particularly in the sealed units, the Fusion Lithium battery is one example of this. One of the main requirements I can see from an Aux battery is the ability to jump from it if necessary and also have a high constant current output if required. So buyer beware, do your research and make sure it suits your needs.
Lifepo4 won't suit everyone, but it suits my needs
Just a thought - but wasn't it lithium batteries spontaneously combusting that caused the Boeing 777 Dreamliner to be grounded for so long?
Circuit diagram is impressive however the text is a bit small to read. Are you able to upload a larger version? Haven't digested it all but I think you said in this thread you have a Paj? You also mentioned about VVA's? Does you Paj have one? If so you will need to remove the link between the battery negatives and tie your camper chassis back to the vehicle chassis.
ECU probs can result if you don't.