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The battery may be failing. Does it indicate a full charge, before you use it? if so, then it isn't dirty contacts or a loose mounting, but rather a battery that is either failing to hold charge or failing to deliver power enough... the normal pattern for the eventual failure of a rechargeable battery.
At 1.5 years, it is several month or six months out of warranty. So repair would be at your expense, not Garmin's. If you think you have a fine touch and fine tools, you might be able to replace the battery yourself, though. Let me know if you are interested in that option, or in the option of having the battery replaced by Garmin or another service co. perhaps. Thanks.