You may say the longest the better.
This kind of answer never ture.
Normally,heated jacket will have three heat seting and,high will last 3-4 hours,mid for 4.5-6,low for 9-12 hours.
For most of the heated jacket,it's powered by protable battery. It's designed to run 3-4 hours in high is quite a balance between using time and protablility. .Run more hours,you need to have a bigger battery. Or lower the heat power consume, which already just enought.
For those out of the range of this figures, be careful.You probably need to buy another battery.
If you do need to play outside all day,you have to buy another battery.
But if you do buy the right one, like a powerbank type heated jacket,it's not engouh to just have even 2.