MDBT42Q on coin cell

@Robin I'll update the docs to make it very clear.

What do you mean by that? The MDBT42 docs page says it accepts 1.7-3.6v range.

By '2v or so' I meant exactly that. If you look at the CR2032 discharge curve the battery is basically dead by the time you get to 2v anyway.

scanning

As @allObjects says, instead of wiring each segment to a pin, you just wire them in a 'grid' - so probably you use 7 IOs to drive your 7 segments and 5 LEDs, and then another 3 IOs to select whether you want to light up the 1st or 2nd 7 segment, or your LEDs.

It gives you a lot of control over the brightness and power consumption, but also saves you a bunch of IOs and makes wiring easier.