18650 lithium battery assembled into a 72V50Ah battery pack needs to take the following steps:
1. Determine the number of batteries needed: A 72V battery pack requires 20 batteries in series (the voltage of each battery is 3.6V), and 5 batteries in parallel (the capacity of each battery is 10Ah).
2. Purchase a suitable 18650 battery: choose a 18650 battery with a capacity of 10Ah, and ensure that the battery brand, model, voltage, and capacity are consistent.
3. Test the battery: test the voltage and internal resistance of each 18650 battery, and screen out batteries with similar voltage and internal resistance to form a battery pack.

4. Connect batteries in series: connect 20 batteries in series, and make sure that the positive and negative terminals of each battery are connected correctly to avoid short circuits.
5. Connect batteries in parallel: Connect 5 groups of 20 series batteries in parallel. When connecting, make sure that the positive and negative poles are connected correctly to avoid short circuits.
6. Perform battery packaging: Assemble the battery in the appropriate battery packaging box to protect the battery and ensure safety.
7. Perform battery test: Before use, the entire battery pack needs to be tested to ensure that it works properly and meets the design requirements.

Therefore, I recommend TEFOO ENERGY standard lithium battery, which is convenient for operators to carry out mobile indoor and outdoor operations. Providing continuous, efficient and stable mobile power supply has become the greatest guarantee for the normal operation of such equipment. The solution uses high-performance batteries, so that the entire battery has the characteristics of high energy ratio, light weight, small size, high cycle life, high safety, and high consistency. The battery is very convenient to use, and the original battery can be directly replaced on site.