Buying a Used Dive Computer: Battery, Sensor and Firmware Checks
A used dive computer is one of the best deals in diving, because the electronics either work or they don't. Here is how to tell which, and what actually wears out.
The three things that fail
Batteries and their compartment seals, depth sensors, and buttons. Everything else on a dive computer is software, and software either runs or it does not. So the inspection is short and specific.
Battery and compartment
- User-changeable batteries: open the compartment. Look for a dry, clean O-ring seat with no white crust. Corrosion here is the single most common reason a used computer floods on its next dive.
- Sealed rechargeables: ask for the age. Lithium cells lose capacity after a few hundred cycles, and a computer that only lasts one day of diving is a nuisance on a trip.
- Factory-serviced batteries: a computer that needs a factory battery change carries a real cost — price it in.
Depth sensor and screen
- Compare it against another computer or a reference at a known depth. A sensor reading a few feet off at the surface will be off at depth too.
- Look for fog or droplets under the glass. Moisture inside means a failed seal, and it will get worse.
- Check every segment and pixel with the backlight on. Dead segments on a wrist computer make a depth reading ambiguous at exactly the wrong moment.
Firmware, modes and logbook
Update the firmware to the current version before you dive it; manufacturers fix real algorithm and sensor bugs in updates. Confirm the modes you need are actually enabled — some models charge for nitrox or trimix unlocks. And read the logbook: the dive count and maximum depths tell you more about the computer's life than the seller's description.
What certification adds
Every certified used dive computer on DescendAgain has its battery and seals checked, its depth sensor verified against a reference, its firmware updated and every button and screen segment tested, with a warranty behind it. That is a short list, which is exactly why a used computer with those checks done is one of the safest used purchases in diving. Start with the used dive gear buying guide if you are building a whole kit.
See all used dive gear in stock, or the service intervals and bench specs we work to.