Don't do this; 3500 lithium batteries are connected in parallel to get 7000 and 600 in series. The final total capacity is still 600 mAh because the capacity of the battery in series is equal to the smallest in the circuit. Additionally, batteries with different properties cannot be used together. There is a special mobile power supply that can be used after installing your lithium battery
18650 lithium battery, 14500 lithium battery, etc.
1. 18650 lithium battery: This is a very common lithium battery with a diameter of 18mm, a height of 65mm, and a capacity generally between 1000mAh and 3500mAh.
2. 14500 lithium battery: This battery has a diameter of 14mm, a height of 50mm, and a capacity generally between 500mAh and 1200mAh.