For what it's worth, I have a Veo 250 (very similar to the Geo). It has been used for nearly 300 dives with no problems and the batteries have lasted reasonable amounts of time. I do not change them on a schedule, preferring to wait until each is exhausted. So, on our last trip, the battery indicator said 'full', but within 2 days and 4 dives, it went to 'empty' during a dive. When I surfaced, it turned on again. So, I used it the next day, no problems. The computer bounced back and forth between OK and empty for another day before dying for good, at which point I changed the battery. My point is, that the depletion of energy in the battery or the computer's ability to detect that depletion may not be linear. The readings are probably accurate, as far as they go, but should be taken with a grain of precaution when odd readings begin to occur on the battery indicator. My guess is that the battery is on the verge of being empty, and the readings are just bouncing around that threshold.