Regarding power consumption, take a look at low power data logger/storage.
Looking at the figures, you may even run the power of the SD Card from a Espruino pin, which lets you keep the battery smaller.
@allObjects started
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.
Regarding power consumption, take a look at low power data logger/storage.
Looking at the figures, you may even run the power of the SD Card from a Espruino pin, which lets you keep the battery smaller.