Summarizing my "research" it seems to be a bit more favorable to keep the battery at a middle stage as long as possible. For another Garmin watch, someone recommended 30 to 70 %, in another source I had found some months ago 40 to 80 %. It said, you should not keep the battery at a completely discharged state for a long time. It is better to charge it from time to time completely, when you need it. However best seems to be to charge it regularly to keep it around 50-60 %.
Generally, charging to 100% is only harmful in long term if you plan to store the watch with full charge. If your intention is to use the charge in short term, then charging to 100% will do little harm.
Have you been able to replace your apparantly damaged unit? According to your comments on other instinct solar topics, your battery did not work well. I hope you found a satisfying solution!
