Welcome to the Forum Fr0stii. If you look at Pi-Top.com website there are several pictures of the Pi-Top[4] please take note there is a small display on top the unit. They refer to this as the OLED, when powered on the status of battery % will be displayed as well as other useful information. When the Pi-Top[4] is plugged in the display indicates the level of the battery % charging. The battery charges relatively fast, I believe about 2 hours. Depending on what you are doing and what peripherals are attached, the battery will last approx. 5 Hours.
As for the Pi-Top[3], unfortunately due to the hardware changes from the Raspberry Pi 3B to the Raspberry Pi 4B the Pi-Top[3] is unable to accommodate the Raspberry Pi 4B. Having said that, there are some users actively making the necessary case modifications to the Pi-Top[3] to accept the Raspberry Pi 4B.
In my opinion, (I am not an employee of Pi-Top), the Pi-Top [4] is the best Raspberry Pi enclosure with OUTSTANDING technical support. If you decide to purchase a Pi-Top product, you won’t be disappointed.
If you have any other question, feel free to post it and someone (a Pi-Top Technician or a customer like me) will be happy to answer it to the best of our ability.
Have a Great day!