Press and hold the increase output button for about 3 seconds (display lights will flash) and the release the button. After the flashing lights the output indicator will illuminate 1-5 lights. This will give you a rough indication of how many hours are on the cell. 1 light 2000+ hours, 2 lights, 4000+ hours, etc.
I have yet to see an IC40 still working after 6000+ hours (not saying it can't happen!).
The flow/temp sensor can also go bad and give that "check cell" light. They are replaceable and certainly less expensive than a new cell.
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