So I got this single Li-ion power bank. It's a 18650, and I wanted to add another 18650 in parallel. I want to use the same circuit which produces a constant 5v. Is it safe to do it that way? in parallel. If no, what is the cheapest & easiest solution?

  • \$\begingroup\$ Show us the photo or schematics, chemistry type, how would you connect them in parallel. Does it have a BMS?.... \$\endgroup\$ – Marko Buršič Nov 13 '18 at 8:26
  • \$\begingroup\$ No, bms, I am just connnect two li ion in parallel. Then connect the negative to b- and positive to b+ \$\endgroup\$ – MasonTM3 Nov 13 '18 at 15:51
  • \$\begingroup\$ What's a power bank seen from your eyes? There are no enough details in your question. \$\endgroup\$ – Marko Buršič Nov 13 '18 at 21:42
  • \$\begingroup\$ those portable phone chargers \$\endgroup\$ – MasonTM3 Nov 14 '18 at 2:20

Not a good idea. The answer is controversial and can be argued both ways based on safety concerns. If you connect two 18650s in parallel, they should be identical and used together from day one. You should not add a second battery after the first one has been used.

See: Building a Lithium-ion Pack

  • \$\begingroup\$ so its okay if they are both discharged. Then charge it after you solder them together? \$\endgroup\$ – MasonTM3 Nov 14 '18 at 2:21
  • \$\begingroup\$ wait not solder, i mean spot weild \$\endgroup\$ – MasonTM3 Nov 14 '18 at 2:32
  • \$\begingroup\$ No, unless you like when stuff explodes and starts on fire. You must start using them when new at the same time. Capacity changes with use. You want to keep the capacity closely matched. Both new from day one. \$\endgroup\$ – Misunderstood Nov 14 '18 at 2:39

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