Like many garden owners I left some external lights up from Christmas (in my case on the trunk of a couple of Birch trees) thinking it would be a nice addition in the summer months as well. But recently one evening I noticed the tree trunk lights weren't triggering at dusk. After checking it out next morning I figured it was a charging issue so took them indoors to charged via USB. After 5 hours of charging I plugged it all back in but the following evening I still had no lights.
Checking on the light strings themselves I noticed they were very tight around the tree. What I'd done to keep the lights from falling down the trunk, was to criss-cross the lights around each other as I wound them around the base of the tree trunk, so making a nice tight fit. What I didn't account for was the 6 month tree growth, so effectively my lights became tighter and then started to stretch until a couple of connections to the LED or the wires inside pulled away from their connections.
So be warned. Sometimes a little sag is better than a tight fit.