First thing—keep it simple. Use a microcontroller with a deep‑sleep mode and only wake it for the bare minimum, like a single sensor read. Turn off all radios unless you’re actually sending data. Second—break the code into tiny tasks. If one part fails, the rest can still run. Use watchdog timers so the whole thing resets if something stalls. Third—save the state to flash before sleeping. That way if the battery hiccups, you pick up where you left off. And don’t forget a watchdog on the battery itself. If the voltage drops below a safe level, shut everything down so you don’t drain it to zero. Keep the firmware size small; fewer instructions mean less power. Finally, test it in a real battery‑driven loop a few times before you drop it in the wild. Simple, hard, and it’ll survive a lot.