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I have an eBike battery pack of 78 18650 cells (13s6p) that I need to charge for storage pending a BMS. I have the following specs from the data sheet:

charging specs

I want to charge the individual cells (of six 18650 each) independently. I only plan to do this once as I plan to have a BMS as soon as possible. I have no way of testing current. I do have a 2A 5v power supply. If I were to put a resister on it to reduce the voltage to 4.5 I assume the current will drop as well. If I did this (tell me if it is a bad idea) how should I alter the charging time to safely charge the cell?

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  • \$\begingroup\$ All will depend on what your "a 2A 5V power supply" is. Does it have a constant (or limited) current mode when overloaded? If you load it with, say, 1 Ohm big wirewound resistor, will it deliver ~2V without starting to smoke? \$\endgroup\$ – Ale..chenski May 1 '18 at 1:33
  • \$\begingroup\$ I doubt it. I was referring to a small wall adapter with a USB charging port. I do have a power supply from a G4 tower. Would that be prudent? I also have assorted tool chargers but they are higher voltage. Do you have any suggestions? \$\endgroup\$ – Jean-Paul McCoy May 1 '18 at 5:21
  • \$\begingroup\$ Charging port is actually good, chargers should have "soft" CC-like cut off. Six cells in parallel can take a lot of current, and it will be limited at 2A. However, there is no "safe way" to use it, unless you watch the charging voltage all the time. You should start with some resistor, 50 Ohm, and check if the 6S battery is about 4 V. If it is, it is already charged sufficiently for storage. If well below, 3.3 or something, apply your charger, even without resistor, and watch for the battery voltage to rise. When it gets to 4.1V, stop. \$\endgroup\$ – Ale..chenski May 1 '18 at 7:31

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