Best way to drain Li-ion batteries prior to recharge?

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I have a lot of Li-ion 18650 batteries that I want to use for a few projects. I'm sure they are all in different states of health and charge, so I figure that draining them (to whatever safe voltage is best) and then charging them would give the best results.

I'm also going to build a charger where I want to incorporate over-charge protection. Can the same component be used for both applications?

If there is a fairly easy process of draining the batt's w/o killing them that doesn't involve building a circuit, I'm interested in that as well.




On a side note - another project related to this...

I'm also interested in building a charger where I can charge at least 4 individual cells (probably more like 8-12) and also a charger that I can charge many cells in series (cells of all the same make/model/age - so they should charge relatively similarly). I want to build in over-charging protection into this device.

I'm considering using a standard ATX PSU as the power source for this device as I can use the 3.3 or 5v for the single cell charge source and then the 12v rail for charging 3 cells at a time (24v is even possible from this unit, although only at ~1-1.5A which is still decent).
 

DC_Kid

Joined Feb 25, 2008
796
i thought Li bats didnt need a drain like the old Ni-cad's did.
charge rate and charge full control is whats needed.
others can correct me if i am wrong
 

dl324

Joined Mar 30, 2015
9,568
Deep discharge of most battery types will decrease lifetime. If you want to discharge batteries, you need a circuit to monitor battery voltage and remove the load when they're discharged to your specified voltage.

You didn't mention how you plan to configure the batteries (single, series, parallel, series-parallel). Anything other than single requires matched batteries for best performance.

Charging batteries in series or parallel is a bad idea.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
Deep discharge of most battery types will decrease lifetime. If you want to discharge batteries, you need a circuit to monitor battery voltage and remove the load when they're discharged to your specified voltage.

You didn't mention how you plan to configure the batteries (single, series, parallel, series-parallel). Anything other than single requires matched batteries for best performance.

Charging batteries in series or parallel is a bad idea.

Anything in series/parallel will be the same model when in a pack and charging.
 

crutschow

Joined Mar 14, 2008
24,056
There's no good reason to discharge Li-ion batteries before charging as long as you have the proper Li-ion charger for the battery you have.
Any discharge just serves to reduce the battery's life.
 
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