matching cells

Let's have some discussion on cell matching techniques.

2. How well are they matched (+-10mv)?
3. How did u match them or did they come matched already?
4. What factors led to the mismatch and how to keep them matched?
5. Importance of voltage and capacity matching

For me, I received 2 panasonic 3100mah 18650 cells from ebay, claimed to be manufactured in July 2011. they come with 10mV mismatch and I matched to 3mV it by using the same slot on the xtra WP 2 II charger.

love to see your replies.

Matching cells ...
The variables = Capacity , discharge ability , and resting voltage from charger ...

Capacity is a DUCK unless you have a hobby charger and can discharge them .
Discharge ability , I use several lights for this [ as they vary in current draw - different drivers etc ]
Anyhow , I aim for 1A 1.5A 2A 2.5A etc tests in various lights ..
What your looking for is variation across a range of current draws , you want cells to be close , low current , medium current and high current .

So if the batteries match well across several tests , Capacity , Voltage after charge , and discharge , you can feel some what safe .
The other thing to watch for :
In your multi cell light , is , to monitor the batteries when using the light before feeling 100% safe ...
Mark the cells for their possition in the light , and see if there is any variation from one cell to the other ..

As high powered flashlights have a tendency to get warm , warmer one end than another ..
And Li-ion batteries are some what temp sensitive , and generally , the warmer the battery the betterthe discharge capability .
So if you have a 3 x 18650 light , and the head is warm and the tail is cool ?
you want to make sure that the battery at the head is not discharging faster than the battery at the tail .
Just possibilities to be aware of , and to monitor for .

If everything checks out , then checking the batteries from time to time to make sure there ok - should be ok ..
Think of it as driving a race car - which requires more maintenance - rather than a family sedan which can get away with less maintenance [ single cell light ]

actually I am using them in series, but with physical position that both cells will likely to experience the same temperature.