The current maximum capacity of the 18650 battery can reach 3500mAh - 3600mAh.
The highest capacity for an 18650 battery is the NCR18650G which clocks in at 3600mAh. A high capacity cell that is readily available is the 3500mAh LG MJ1.
But the most commonly used 18650 batteries on the market have capacities of 2000mAh, 2200mAh, 2500mAh and 2600mAh.
Li-Ion batteries are the most widely manufactured batteries in the world. If you don't think it is that common you surely wont believe that 40% of the worlds batteries are Lithium Ion. They are used in Laptop, Power tools, robots, electric vehicles, solar grids and almost all devices that requires to store energy.
currently lithium ion battery mainly comes/makes from China, china should make at least 80% of the total lithium batteries.
This Chinese manufacturer does all kinds of Lithium batteries and is also doing custom builds:
Benzo Energy · UFine Technology Co.,Ltd
Their online website: ufinekorea.com
They are a Chinese professional lithium battery manufacturer.
They can customize the 18650 battery packs you need according to your requirements.
