Why do 100k people need a car battery monitoring app? The dial is right on the dashboard of the car, what does this app possibly do?! And drain your phone battery continously as well, is that really worth the ability to see on your phone screen what your dashboard already tells? And if it's for a stationary battery, why not just analog volt meter dial?
Sorry for complaining, but it's so hard to find standalone devices that don't require an app nowadays (simple example: try finding an LED lamp where you can choose the light color that allows doing it with a button on the lamp itself without app - I found one but it was non-trivial and it still doesn't allow color cycling without app). If people wouldn't prefer this BS, it would be easier to find sane electronics/electrics again.