Just thought I'd better point out that I had very similar problems until I upgraded to the latest firmware version, 2v11. After upgrading to 2v11, the battery life has been much better (and stable). The firmware upgrade can be a little problematic, however, so be sure to read the posts related to updating the firmware if you run into any issues.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Just thought I'd better point out that I had very similar problems until I upgraded to the latest firmware version, 2v11. After upgrading to 2v11, the battery life has been much better (and stable). The firmware upgrade can be a little problematic, however, so be sure to read the posts related to updating the firmware if you run into any issues.