Long life logger using eeprom and bluetooth

Hi - yes, it's definitely the right place for completed or in-progress projects :)

Q1. Is that a reasonable approach?

EEPROMS are good but often aren't that big, but as @allObjects says there's external flash chips, or even on-chip flash on the Pico or original Espruino.

or I believe that some of the SD cards don't draw much power at all. It'd be a matter of testing, but I imagine that if you found a small capacity card (64MB, if they still make them?) power consumption would be pretty good.

To access the data when nearby with BT I wanted to use the modules I have, HC-05

You may need to change some settings on the module itself, as (at least when connected) it can end up drawing quite a lot of power. If you google HC-05 SNIFF mode you should find some info on this.

its a simple matter of soldering that to the prototype area of the Espruino, but how/where would I then attach an eeprom?

The bluetooth goes on the opposite side of the board, leaving the prototype area clear :)

Q3. Assuming that is all physically do-able, could I then command, via BT the reading of the eeprom, and if successful, the deletion of the eeprom to empty it? (I am guessing these would be js functions/classes I'd call over BT)

Yes - actually by default, when USB is disconnected Espruino puts the JS console onto Serial1 (which is connected to bluetooth), so you can actually just interact with it as normal. For instance issueing myFunction()\n will call a function of that name.

Oh, and being able to understand remaining battery life would be a bonus too...

For this, you'd probably just need to do some tests to figure out how much power the board was drawing and just guess based on that.

However you could attempt to measure the battery voltage, but the depends a bit on the battery (and also the temperature I think)