@Mellow Hudson Mike posted:...
2.) Charge -- Wait for the internal rechargeable battery to charge. If the unit has been sitting for months this may take a couple hours. If it's only been a few days this will be quick. If it's been many years you probably need to install a new battery (the so-called "green" battery from MTH) before following Step 1 above. In a pinch you can use a common 9v alkaline battery, but only temporarily and for only a short period, to see if the unit is functional.
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Great info in that post, but want to add...
Quite possible that the old battery won't hold a charge. Strongly suggest replacing the battery with a BCR for long-term reliability.