Charging 2x Li-on 18650 Batteries In Series
Specs

Short circuit protection

Overcharge protection

Over-discharge protection

Overcurrent protection

Overcharge Detection Voltage: 4.25-4.35V±0.05V

Over Discharge Detection Voltage: 2.3-3.0V±0.05V

Maximum Working Current: 3A

Transient Current: 5A

Operating Temperature: -40-50 degree

Internal Resistance: Less than 45m Ω

B+ B-: The interface of battery core

P+ P-: The connector of battery board

MB: The connection point between the batteries

B+: Battery V+ Positive

B-: Battery V- Negative

P+: Output / Charging V+

P-: Output / Charging V-

Size: Approx. 36x6x1mm/ 1.42&quot; x 0.24&quot; x 0.04&quot;




Engineering Assumptions


Vsource min &gt; for 2 cell OVP = 8.8V max.
Vsource max &gt; due to Current limit and VI drop thus heat rise from losses


9Vdc 3A seems to be an optimal solution depending on cell ratings.