Leisure Battery Upgrade

Hello and welcome, please introduce yourself.  
Much has been written in other places on this subject but Imo the lithium may need a different charging profile than a lead acid, I would email Sargent with the model of your charger, your solar and see what they recommend.
Rich..

I presume the reason for the capacity upgrade is for off-grid capability. I also presume that your vehicle does not have a smart alternator. I can only speak from my experience with my 2019 Boxer based Kingham with EC700 and non-smart alternator, which I upgraded to 225 AH of flooded lead acid batteries about 15 months and 10,000 miles ago

If you upgrade the battery capacity you will probably want to be able to charge the extra capacity as well, and make use of the lithium battery’s ability to take a larger charge rate.

1. On EHU. In my case the standard Sargent EHU charger remains in place at the moment. It does little to effectively charge the bigger batteries, either simply due to its low capacity (20amps?) and/or due to the wiring sizing. I have not addressed this as yet since we hardly ever use EHU but in the fullness of time it will be upgraded to perhaps 40 amps, and all associated wiring will be upgraded, which will probably mean bypassing the EC700 and charging the LB direct. It might also be the case that your present charger cannot be configured for lithium; you would need to check.

2. Charging from the vehicle engine alternator. On my Kingham with split charge relay integral to the EC700 the proportion of the alternator output that was reaching the LB was minimal, again probably due to low capacity wiring and/or design avoidance of risk of excess heat within the CPU. The fact that there was a 20 amp fuse on the charging connection to the LB tells you something! My solution (for non-smart alternator) was to fit a separate high capacity dual sensing voltage sensing split charge relay (DSVSR) and much heavier charging cables between VB & LB, wired entirely independently of the EC700. An alternative would be a B2B charger but that is more complex, more expensive and will require the Sargent split charge system to be disabled, which may be difficult. With my DSVSR the alternator charging function whilst driving very significantly improved.

3. Solar.  Whether or not you upgrade your solar capacity (I did, to 350 watts), in my case the standard Sargent solar installation was doing little or nothing due I believe to solar controller quality and cabling issues. At the least you would gain better benefit from your enhanced battery capacity by fitting a better solar controller, more suitably wired directly to the batteries.

4.  If you go the DSVSR route then you only need to connect your EHU charger and solar controller to the LB since the DSVSR works both ways. You only need to charge your LB, and the VB will automatically be charged concurrently. This simplifies wiring and widens your choice of solar controller and EHU charger to include the most efficient Victron MPPT solar controllers.

None of the above (apart perhaps from EHU charger compatibility) actually prevents you from making the battery upgrade, but I suspect from my limited experience that the extra battery capacity will not be properly utilised without parallel improvements to your ability to replace the charge.

From Sargent website

https://sargent.zohodesk.eu/portal/en/kb/articles/i-would-like-to-fit-a-lithium-battery?fbclid=IwZXh0bgNhZW0CMTEAAR0UDSagVATXkLSBrraJSO8xEmCqHGf5ZEti-6Czw6PLu3DSsZ9gvVuQiyM_aem_AcDF70SARCLKxu3oUEXU5O_EJUv_qxBB9OqRzGF01KpZwdU0Vmmqk3T2Boya5kkW_w9wOB_0sDxkQBzdfoKi4szf

Installing a DC to DC charger with lithium is a must, smart alternators on Euro6 engines are not compatible with charging lithium & you’ll end up killing your alternator, so you must have a split charge relay fitted along with a DC to DC charger.

The split charger can be disabled in the settings on the EC700 with firmware CP49 for the control panel and 38 for the charger.

To get to the setting long press the settings option on the panel and a load of additional settings should be available.