Lithium replacement.

Its a shame the hardware cant be updated on the charger.  

The only things I noticed were that K1 may actually be redundant.  Connecting Vin and Vout on the DC-DC charges wouldn't be a problem, I think.  Perhaps someone with more knowledge of these could help? 

Is K4 needed? The negative side may all be common already? It was on my 415.  

The feed from the service battery is probably already fused, but not shown, so additional fuse on the mains charger to DC-DC charger may be required. 

There is the possibility that the engine could be started while on shore power so there could be a point at which the start battery is directly connected to the service battery.  You could run the negative to the ACR through a NC relay operated via SW1 for belt and braces.  

This is quite a lot of heavy duty cabling and the relay(s) will need to be pretty beefy to cope with the current for the inverter not to mention the additional fuse(s).  So a reasonable amount of work to connect the mains charger to the service battery via the DC-DC charger. From my experience, so far the AGM, setting on the mains charger settles to about 92% charge (the BMS takes care of any anomalies during initial bulk and absorption phase) for the Lithium so by keeping the cable changes to a minimum by leaving the charger directly connected to the service battery, its pretty near factory set up, I have not had an issue with this.  The short period of motoring I have when leaving shore power usually brings the service battery back to near 100%.  

Would it be worth keeping it simple first and see if the additional work is needed?  You can always make the changes later? Just a thought?

That is a good point, I'm not sure if the alternator/start battery would be happy about the possible load let alone the cabling/fuses.

It may be wise to add another relay to prevent this from happening, triggered from SW1 as mentioned in my earlier post, the belt and braces approach. Not adding the relays and keeping the charger directly connected to the service battery avoids this issue. Another factor to complicate the decision making process!  

The inverter will be connected to the alternator directly currently but also to the service batteries.  The service batteries will supply the required current when the alternator reaches its maximum.  However, the new set-up removes the service battery leaving only the start battery and alternator to take the load. I doubt the cabling/fusing is capable of supporting this and its probably not something I would like to do in any case given the loads involved and the strain on the alternator.  Don't forget that at 2KW the draw at 12v would be over 160A.  I would make sure that in the proposed configuration the inverter is prevented from drawing exclusively from the alternator and start battery.  Because of the setup you effectively prevent the use of the inverter with engine on.  It would be possible to add another set of heavy duty relays for this but its getting complex.

Something else to consider is that you may forget to switch off SW1 with the current setup, as I mentioned , connect the service batteries direct to the alternator but if this is locked out with an additional relay for safety, forgetting to switch off prevents the service batteries from charging.  Not a big problem but another thing to consider. Anything that needs manual intervention will always fail at some point. (Don't ask me how I know this!)

It will be a lot simpler, and almost cheaper with labour and components, to replace the inverter charger with one that supports Lithium if using the AGM setting isn't sufficient to meet your needs rather than a lot of additional complexity. I would still be tempted to keep the current charger directly connected and see how you get on. You might even be able to 'tinker' with the AGM profile a little in the software to make it a little more compatible?

Would be really interested to see what you decide and how you get on as I'm considering adding a bigger inverter to replace the factory 350W unit. So inverter or new charger inverter will be my next decision. 

This is with the Inverter "ON".  The stuff in the grey box is inop, and the big contactors just reconnect the batteries to the inverter.  I'm a mechanical engineer, so this is somewhat mysterious to me... but does this make sense?

The only difference here is that the 12/24 DC-DC charger is also disconnected in Inverter mode, so there is a risk that if I leave it on then it won't get charged.

I have it shown here as a discreet switch.  I'm looking to see if there is a way i can trigger it from the same control panel as the inverter/charger, so it works automatically when the VEBus panel is switched to inverter.  

I'll also add that my use case is different - I spend a lot of time at Marinas plugged in, so that's why i wanted to make sure when on shore power the LiFePo4 batteries were being charged correctly...