Hello,
For Advanced Strategy, there is a guide written by iGP Moderator, Gustavo Heiden, which explains how AS works and the correct ways to set it in different scenarios.
Advanced Strategy Guide link.
The power battery you see in races is boost which allows you a speed boost when pressed (similar to a push-to-pass system). Be careful when using it as it is not recharged during a race, so once you hit 0%, you have no more for the rest of the race.
Further details about boost can be found in section 2.7 of the iGP Manager rules and regulations which I will link below.
iGP Rules and Regulations
"Boost and DRS are available to all teams and are upgraded in the Technology HQ. They are used in the race only.
DRS (Drag Reduction System) - A driver-activated overtaking aid which makes the car accelerate faster by opening the rear wing on the car to reduce aerodynamic resistance
Boost - Also known as KERS, boost is only charged once in iGP Manager and should be used strategically throughout the race. When the manager is present they will control boost, but when they are not the driver will control it."
Additional information about both Advanced Strategy and boost may also be found in the 2022 iGP Manager guide, written by Rhys James -
2022 iGP Manager guide
I hope this answers your question, but if not, or you have further questions, feel free to comment below.