Building a waterproof GPS tracker with 6 months battery life

I designed and deployed a cellular GPS tracking system for a kayak rental operator in Norway. Four prototypes are in field testing, with custom firmware, remote updates, and a live fleet dashboard.

Karbo Labs tracker mounted beneath the deck rigging of a rental kayak — Field prototype on a rental kayak.

Makerdiary prototype connected to a Nordic PPK2 for power measurements — Power measurements on the Makerdiary variant.

My work spans hardware integration and enclosure design, Zephyr/C firmware on the nRF9151, cellular telemetry, OTA releases, and the backend and map interface. The devices use GNSS for position and an accelerometer for motion-triggered wakeup and orientation reporting.

Power consumption is the main constraint: the target is a six-month rental season on a 10 Ah battery. On the Feather variant, I measured 4.4 µA in System OFF and 5.5 µA between reports. GNSS acquisition and cellular transmission dominate the remaining budget. Full-season endurance is pending field validation.

I built a robotic motion jig and combined it with PPK2 measurements and remote firmware updates to automate physical testing. This gave AI-assisted firmware iterations a measurable feedback loop on the device: change the code, exercise the hardware, measure current draw.

The testing setup. Watch on Instagram.

Field telemetry exposed false inactivity decisions during smooth kayak movement and LTE outages after repeated modem reconnections. I adjusted motion thresholds and changed the modem lifecycle to retain registration with power-saving mode, then deployed the firmware remotely.

The current hardware uses development boards in waterproof enclosures with 3D-printed shells. Field validation, charging access, and mounting are the next steps; capsize detection remains experimental.