Huawei Mate 20 has a 4000 mAh non-removable battery.
For any assistance related to removing/replacing the battery, you need to visit service center.
You can find a service center near you from here.
Below video shows How to change non-removable battery:
You can look at complete specifications here: Huawei Mate 20
Yes, Huawei Mate 20 does support Reliance Jio Sim in sim slot 1. With Reliance Jio 4G VOLTE network, you just have to pay minimal data recharge amount as minimal as Rs 399 for 84 days. You also get unlimited calls and SMS along with the plan. Adding to its seamless benefits, it offers nationwide free roaming.
You can know some hidden features of JIO sim here:
You can find complete specifications here: Huawei Mate 20