July 27th, 2009

NiTek X Battery Discharge – Not a Service Issue

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We have received several NiTek X computers in for service and all they really needed was a new battery. I asked the programmers how the battery indicator worked to get a better understanding of what’s happening. The chart below gives you an idea of how the indicator works.

The important thing to notice is the discharge curve after 50 hours of normal use. This can be accelerated by using the backlight for long periods. When you notice the battery indicator has moved from full it is really a notice that the battery should be changed within the next 20 hours of dive time. If you don’t, the NiTek X could go dead during a dive.

The battery indicator will be good until the battery goes through roughly 3V – so the battery scale moves between 2.9V to 2.4V as empty. The curve on the batteries are like this:

CR123A Battery Discharge

CR123A Battery Discharge

So anything above 3V is just an artifact of a fresh battery.

If you measure a new battery it is common to see 3.2V even with some load. In sleep the Nitek X uses a very low current so the computer will show a curve like the above, yet flatter. If the computer is in standby a long time the battery will be at a higher voltage than it would after some use, because there was no load during sleep. CR123A also does self-discharge about the same rate as the NiTek X sleep current.

So if the battery gets low and the diver takes it out of sleep it might just drop the voltage quickly and die, or fail to start after a long time. Or if the diver dives with backlight at the end of battery life and then the NiTek X goes to sleep, it may not turn on the next time.

Before sending your NiTek X to us for service, replace the battery. And keep an eye on the indicator.

Lamar

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