ReefNet - Sensus Ultra

A single, reliable, easy to use electronic dive logging device.

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A Battery Warning Means You Are Diving On Borrowed Time!

The nature of the lithium chemistry batteries used to power virtually all dive computers and digital bottom timers on the market has important consequences to battery life and in particular to battery warnings. That is because while lithium chemistry batteries have a very long life, it is extremely difficult to detect when they are nearing end-of-life. Lithium batteries often change from delivering full power to nearly dead in a very short time. Detecting the end-of-life is made even more unpredictable in dive computers, because they draw very little power at the surface but the power requirement increases significantly when diving.

In our experience many different brands and models of dive computers and digital bottom timers, without warning, become very erratic as a result of reaching near end-of-life on the battery. Sometimes an instrument will issue a battery warning during the dive, but on the surface after the dive the battery warning may clear. Sometimes, the first symptom instead of a battery warning might be an inaccurate depth reading which will result in inaccurate decompression times or other bizarre readings. Just to be clear, this problem is associated with the battery chemistry, not the instrument, and is true regardless of the brand name.

  • Learn what the battery warning indication is for your dive computer or digital bottom timer.
  • Never begin a dive with an instrument showing a battery warning.
  • Always have a backup should your primary instrument fail, either a second computer or a bottom timer and tables.
  • If you notice a battery warning during the dive, do NOT trust the instrument accuracy, switch to your backup solution.
  • Best practice is to occasionally compare the primary instrument to the backup, in case there is no battery warning.
  • For models with rechargeable batteries, carefully follow the manufacturer recommendations as to best practices for maintaining and/or recalibrating the charge in the battery.
  • For models with user changeable primary batteries, change the battery at the minimum factory recommended interval for your model, regardless of number of dives.
  • Our recommendation is to always change the 'coin' type lithium batteries annually.