Nowadays, lithium-ion batteries are very popular because of their high energy intensity and at the same time compactness. The most popular size is 18650, of these elements make up the laptop battery.
Samsung Li-ion batteries with a capacity of 2600 mA * h have gained a good reputation by confirming that the real capacity matches the specified by measuring with special testers like Imax. They can give relatively large currents without harming themselves, the internal resistance of the new 18650 can declared by the manufacturer is about 60 mOhm. After fully charging one element at its terminals, the electromotive force should be 4.2 V.
Samsung 2600 rechargeable batteries can be used in powerful flashlights, cameras, radio-controlled toys, portable chargers and others electronic devices. It is 18650 larger than an ordinary AA element and has a radius of 9 mm and a height of 65 mm, weight 0.044 kg. It is also worth noting that accumulating elements of this type do not tolerate cold well - this must be taken into account. Sometimes a protection in the form of a small scarf is built in, which warns the element from excessive discharge and extreme currents, but these instances do not have it. In fact, sometimes because of this board, the battery does not fit into its compartment and therefore its absence is not always a disaster.
When creating electronic devices, you can safely use 18650 batteries as a power source. If a voltage of more than 4.2 V is required, then in this case the elements are connected in parallel and use a voltage converter to increase the voltage to the required value. It is also possible to connect banks in series with the obligatory use of a balancer, as these chemical energy sources have variations in characteristics even in one batch.
Cost: ~ 177