The most important sentence about this app is one about what it does not do.
MultiVolt is a display and a log, not a safety device
The app reads measurements and presents them. It does not intervene. No switching commands go over Bluetooth — it toggles no MOSFETs, disconnects nothing and writes nothing into the memory of the BMS. To Ective batteries it sends nothing at all, because that protocol is never polled in the first place.
Low-voltage cutoff, overcharge protection, overcurrent and temperature disconnect must be configured in the BMS and work without a phone. A flat phone, a closed app or one metre too much distance must never be the reason a battery is damaged.
MultiVolt does not run in the background and sends no notifications. Anyone expecting a warning during the night will not get one.
If a BMS reports nothing about its protection states, MultiVolt shows "unknown" — not "OK". That applies in particular to Ective batteries, which say nothing on the subject at all. A green tick there would be a lie.
MultiVolt does not measure anything itself. What you see is what the battery reports, with its accuracy and its errors. A badly calibrated state of charge does not become correct by passing through the app.
The app only sees what it witnessed. Across gaps in the connection nothing is extrapolated, because guessing would be worse than a gap.
Work on vehicle electrics belongs in qualified hands. This website and this app provide no instructions for it and replace neither the installation requirements of the battery manufacturer nor the applicable rules for electrical installations in vehicles.