Last weekend while I was diving with a buddy we got to where we were going to exit and I looked down at my computer which was indicating that I had already surfaced from the dive and that I was enjoying a surface interval. Now, as I was a good 20 – 30 feet below the surface I was pretty sure I wasn’t at the surface so I punched a bunch of buttons on the computer thinking it might come to its senses.

It was only then that I noticed that the battery meter was registering in the “need to be replaced mode.” The funny thing is that for the last several years I’ve carried a backup computer somehwere on me just in case but almost felt foolish for doing so. Not this time though. I reached in my drysuit pocket and my backup was working perfectly.

I had remembered what my now impared computer had said was my maximum depth during the dive (and had a general sense for the total dive time) and compared that to the backup and they seemed to match so it was a relief that I hadn’t been getting faulty readings and had been diving much deeper than I had thought I was but still an eye-opener that just because a computer goes into dive mode on descent doesn’t mean that it’s got enough juice to see you through the entire dive.

So the lessons learned here are:

a) Check your computer’s batteries every couple of years or so.

b) It’s always good to have a backup.

On a side note (that I almost feel foolish admitting); on my backup computer it has a voltage reading. If it goes below 2.8 I know to replace it. On my primary computer it has a bar graph that displays when you first begin your dive. I always check the voltage numbers on the backup and replace at 2.8 even though it could probably go all the way down to 2.0 before it becomes an issue. On my primary, I don’t think I ever really checked it because it only displayed for a few seconds when going into dive mode at the beginning of the dive. That’s a mistake I won’t make twice