Comment by LeifCarrotson

Why not both? I'd love an error LED to tell me something's wrong, maybe (maybe) with complicated blink codes that I can count and recount to determine which cell is bad or what action to take, but I also want a Bluetooth app to access the actual data: live cell voltages, currents and temperatures, estimated storage capacity and cell health, lifetime charge cycles and total power delivery... Give me all the data!

I don't want to increase the cost and complexity, and reduce the runtime of the thing with an onboard tiny LCD and an array of buttons to navigate menus. The interface could be available over a Bluetooth app, or or a self-hosted webpage, or make it show up as USB mass storage or a USB virtual serial port, or an actual RS232 or RS485 or TTL serial port, or I can grab it off a storage device with an EEPROM clip, or hook up my Tag-connect cable and a bus pirate and get I2C or SPI or whatever unnecessarily custom UART protocol you want to invent, or I can buy your dedicated HMI device with the LCD and buttons connected by a custom cable (don't want to buy yet another, I already have too many kicking around from decades of work with random industrial VFDs and PLCs and stuff), or I can hook up my MSO to some test pads and read the signals directly... But not everyone has all those tools and cables.

Like it or not, the standard has become a Bluetooth app. I wish the standard was a self-hosted webpage, so I could connect my laptop to a buried RJ45 connector, set a static IP to point my NIC at the right subnet (or the device could embed a router to assign my laptop a compatible IP over DHCP, but most don't), or I could turn on an integrated wifi adapter in the device, ignore and revert the protestations of my device and OS that the connection was unsuccessful because it can't ping connectivitycheck.android.com or captive.apple.com or msftconnecttest.com or whatever through the battery pack SSID. But by the time your user manual tells the user to go to their network adapter properties and set their IP address to 10.10.0.2 (on their iPad, LOL) you've lost most people long ago.

Like it or not, the standard has become Bluetooth and an app, and not without compelling if frustrating reasons.