How to make an 18650 storage drainer?

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How to make an 18650 storage drainer?

I have a number of 18650 cells which I would like to be able to keep at 3.8V for long-term storage.

I have a Tenergy unit which I have used for this with one cell at a time. It is capable of draining at 1A.

I have a bunch of cells now and I need a more convenient way to discharge them than this method. Maybe a 4 or 8-bay unit. I’d charge to 100% and then stick the cells in the parallel and do a 1S discharge (right? Or should I make a balance discharger so I could start with cells at multiple voltages? My Tenergy could support that).

Most of the 18650 holders I see on Amazon have little pins sticking out of the bottom of them—they look like they are meant to go into holes and be soldered on to something, but I’m not sure what. I have a soldering iron. Maybe I could use magnetic contacts so I could drain various sizes? I have some neodymium magnets, but they seem to be really poor conductors.

Things I’m looking for in a list:

  1. 4 to 8 cells simultaneously
  2. handle protected (long cells) and unprotected
  3. fairly durable
  4. leads are thick enough to handle current without getting hot
  5. easy to get the cells in and out (the cells won’t live in here—I need to get them out so I can put the next batch in)

I think I’ll have to make this thing, but I want some parts as a starting point.

Lightbringer's picture
Last seen: 49 min 19 sec ago
Joined: 08/30/2016 - 14:12
Posts: 17110
Location: nyc

Well, what you can do is wire up all the holders in parallel but through power resistors to a common point. This way, all the cells would equalise to the same voltage given enough time.

Then take the common point and ground, and wire it up to a “dummy cell” and discharge that to 3.8V.

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

jeff51's picture
Last seen: 25 min 14 sec ago
Joined: 03/26/2019 - 17:36
Posts: 1517
Location: Middle of Texas

Or run them down in lights.
Then use a 8 bay charger and set it for LiFePO4 voltage.
All the Best,

Last seen: 1 hour 5 sec ago
Joined: 08/30/2014 - 16:00
Posts: 1882
Location: Swampland,La

I have been testing and storage charging batches of cells for a couple months now ( over 2000 cells) I made up a series holder a 3S2P of 4 cell holders (holds 24 cells)with a balance lead and I use a Q8 hobby charger —with this charger you can pick storage mode then adjust your shut off voltage —- I pick 3.85 volt and after they settle in by the next day they’re 3.83v —- It’s a lot easier to have the cells lower voltage and charge them back up than to discharge in storage mode