Bought two Bounces, one last for 24h, the other for 8h...

Hi,

3 weeks ago I bought two new Bounces (directly from Garmin) for my boy (9) and girl (8).
The watches itself work good and the kids love them, but....

The watch from my son lasts for about 24h, loosing about 5% per hour (not great but acceptable).
The watch from my daughter lasts for only 8-10h, loosing about 10-12% per hour.

So she can't even use it at the time she really would need it, when school is finished.

Both watches have the exact same setup... Locked or school from 8:10 in the morning until school is finished at 16:30 (4:30pm).
Both kids visit the same school and their classrooms are next to each other.
Both watches have the latest firmware.
Did already reset the watch.

We are located in France.

Could the reason be, that my daughter's watch always shows a worse radio signal than my son's? Always one bar less.