Thanks to MW_eUP and jesseb4me on the myenergi forum, here are a couple of suggestions on how to you could install a hybrid battery system to improve the way it works alongside your myenergi products.
To have the Zappi not drain my house battery, which is a DC coupled battery with a hybrid solar inverter, allowing me to manage my house electricity generation and storage optimally.
To still have the Zappi make use of excess solar power when available.
The hybrid inverter sees the Zappi as part of the 'house' load, so any time the Zappi is charging, the inverter tries to meet that load using my house battery.
You can -kind of- get around this by scheduling the house battery to charge at the same time as the Zappi, but this is a cumbersome approach that doesn't really work with the Myenergi Account automating the cheapest times, especially on the Agile tariff.
Mine would also interfere with the Eco+ mode on the Zappi even with an 'Export Margin' set, as when excess solar starts, the Zappi kicks in also drawing a tiny amount from the battery. The Zappi would slowly scale back to the export margin, however by this time the battery has decided to use solar to replace that tiny amount, so there's not enough solar excess... rinse and repeat
My original wiring setup had the solar hybrid inverter connected to a secondary consumer unit, which was originally fitted to supply the Zappi.
This means that no matter what I did, you could never separate the inverter's view of the Zappi draw from the rest of the house load.
My installer (after significant humming and debating if it would work) reworked my inverter to connect through the main house consumer unit.
This meant that the inverter CT clamp could go around the tails for just that consumer unit, and not the tails feeding the Zappi!
The solar inverter can still monitor and manage the maximum amount being 'exported' (important for some DNO approvals), but now it doesn't see that the Zappi is taking power from either that excess solar being exported, or from the grid.
The Myenergi system still sees the entire import/export from the grid, as well as the flow to/from the hybrid inverter.
As the solar inverter 'export' may be limited by your DNO (often to 16 amps, ~3.6kW), this limit will also be the maximum amount the Zappi can take from your solar.
This is because your inverter will no longer 'see' the Zappi as part of the house load, so thinks that power is going to the grid.
For my solar array size this isn't an issue, however if you have a large solar array, you may find this limits your Zappi charge rate too much.
For the same reason, the logging and statistics from your solar inverter won't show your true 'export' - some of the power it thinks has gone to the grid, has actually gone to the Zappi.
However, the Myenergi statistics should still show the correct figures for everything!
It also means that if, for whatever reason, you WANTED to charge from your house battery, then you would need to schedule your house battery to discharge, and let the Zappi take up that export.
I hope this help others who have (or are considering getting) a hybrid inverter installed, and who also get frustrated that plugging in their EV drains the house battery right away!
It would be cool to see a DC battery monitoring hardware option from Myenergi (if that's possible!) or perhaps a software solution with integration with different inverter API's, but that's a very complex approach...
Two basic possibilities of interaction with an Battery (AC or DC) depending on the installation