Pre-purchase Q: Flexboss21/Gridboss register write-endurance + split 400A / dual-200A-panel setup

Looking at a FlexBOSS21 + GridBOSS system but haven't pulled the trigger yet — want to work through a few Modbus register questions first since my planned control setup depends on the answers.

One thing up front so nobody assumes the usual setup: my service is 400A, split into two independent 200A panels that both feed toward the meter. The FlexBOSS21/GridBOSS would land on one of those 200A panels (the backed-up one). The GridBOSS's own CTs only see that panel — they have no visibility into the second 200A panel at all, since it's a completely separate panel that only reconciles with the GridBOSS's panel out at the meter. So from the inverter's point of view, any load on that second panel is indistinguishable from grid export. I'd be adding an Acrel ADL400 on that second panel to actually see its load, and feeding that into a local Modbus RTU loop (RS485, no dongle, no cloud) to try to serve both panels from solar/battery before buying anything from the grid, without exporting stored battery energy in the process.

Working off the 18kPV-12LV Modbus doc plus the community FlexBOSS21 register map (@snarfattack's ESPHome work has been a huge help here) since I know a full official register map for FlexBOSS21/GridBOSS isn't out yet.

Questions, roughly in order of "this determines whether the whole plan works":

- **Registers 138–143** (the 0.1%-resolution *PowerCMD registers — ChargePowerPercentCMD, DischgPowerPercentCMD, ACChgPowerCMD, ChgFirstPowerCMD, ForcedDischgPowerCMD, ActivePowerPercentCMD) — anyone know if these are RAM or if they write through to EEPROM/flash? I'd be hitting these roughly every 15s (~5,700 writes/day) to track the second panel's load, and that's a lot of writes if they're not meant for it.

- Does **Charge Priority** (reg 141) pull PV away from backed-up loads to hit its target, or does it only grab PV that's already surplus to load demand?

- What's the **kW reference for 100%** on the 138–143 block for FlexBOSS21 specifically?

- Is **ForcedDischgPowerCMD** (reg 142) the *total* discharge target, or an *add-on* to whatever's already discharging natively for EPS/backed-up loads?

- Is **10% really the floor for EOD** (reg 105) on-grid like the 18kPV doc says, or can FlexBOSS21 go lower?

- Any general guidance on **write endurance** for holding registers — and specifically for reg 103 (MaxBackFlow)? Since the second panel is invisible to the GridBOSS anyway, my plan is to treat MaxBackFlow as a static ceiling rather than something I write dynamically. Sanity check that's the right call?

- Has anyone here actually run a **GridBOSS-invisible second panel** on a split 400A service like this? Trying to figure out if I'm about to hit a known edge case or if this is well-trodden ground.

Will post back with whatever I find out / whatever I end up testing — seems like it'd help anyone else with a similar split-panel setup.