How many hours before they gave out?
Here's what happened. I used the system Friday night and it worked fine all night 9pm to 1 am, but I left the receivers on overnight.
I retrieved them earlier on Saturday and took them home to charge. The manual states 2 hours to fully charge which seems about right (the light stops blinking when it's fully charged). Saturday's show was very unusual, where the band first played from 5-7:30, then returned to the stage for a 9:30 to 1 am show. I lost one tree at about 11 pm and the other at about midnight (I had a spare ready to go). So at best I got exactly 8 hours out of the receiver.
I'm just going to wire up a charger to each tree and be done with it. If I were buying them today, I would get the non-battery units which are smaller.