Battery recharging Question

My Ultra 2000 has been heading back to recharge when battery level is over 70% (30% used). Never did this before. I have charging set to recharge when it gets to 15%. Any ideas why it’s doing this? I clean it after every use and just replaced blades yesterday.

Hello, thank you very much for your patience! Could you let us know if the local temperature has been extremely high recently?
Excessively hot ambient temperature will trigger the motor overheating protection, making the robot head back to the charging station early for cooling and charging. If the unit keeps working on slopes for a long time, the motor load will increase significantly, which makes this protection mechanism activate even when plenty of battery remains.

It’s been in the 90’s off and on for two weeks. It’s cut the grass in hotter temps than today without returning to charging station earlier. Besides, it’s the summer and it should work in hot weather… right?