I'm getting some feedback on how I make up MY 4S 2800mah Li-ion packs from 18650 cells that weigh right at 197 grams
It measures 40mm square by 73mm long not counting the wires.
 
Again..this is how I assemble them.  I KNOW others do it differently.  I KNOW soldering is not recommended. I KNOW someone else may have a better idea/way.  Take it for what's it worth.  This is NOT a "How to". This is a "How I do"......

I use Molicel P28A cells.  These are 2800mah capacity with a 35A max discharge rate.
I solder all battery and wire connections.
I use size "BGA" solder wick for the battery interconnections.
I use 16 gage Castle Creations wire leads terminating to XT30 connectors.
All soldering is done with a 40watt iron and a chisel tip.

1st-I clean each battery terminals with a few swipes of scotch brite and then wipe 'em with a bit of lacquer thinner.
2nd-I pre-tin the cell terminals with a bit of 60/40 rosin core solder.  It only takes a few seconds to achieve an acceptable blob.
3rd-I assemble the 4 batteries into my own designed 3D printed cell holders that allow a slight press fit onto the cells.  The back and front spacers are different from each other as the front requires an opening to allow the 16ga leads and balance tap wires to exit.  They also allow cooling air to circulate between the cells and allows thru the center air flow.    There is also trenches for the interconnect straps and clearance for the balance tap wires.  The cells are only slightly warm after a 5 minute flight consuming @1800mah (@22A average).
4th-I solder 3/4" long pieces of the solder wick to the cells.  2 straps on the back end and only 1 required on the front end.
5th-I then solder the battery leads onto the plus and minus terminals that already has the XT30 connector attached to them. This reduces the chance of a short circuit.
6th-I then solder the balance leads to each cell using the positive terminal "side" where possible. This allows a quicker easier solder operation.
7th-I then get my voltmeter out and verify the balance tap wire sequence and the polarity of the XT30 connector.
8th-I then use medium CA to attach the front and back end caps. These keep the connections safe from shorting on something.

Attached photos show how neat and clean MY assembly is with the 3D printed parts.
That's how I do it.  Now hopefully after 300 cycles on it I'll still be happy with the pack.......

Link to .STL files:  https://www.thingiverse.com/thing:5739042

Clean work!  Thanks for sharing your build.

18650 is diameter by length. 18 dia by 65mm long.
Can you guess what a 21700 cell is??

Probably start your own thread on what cell vs another cell 'eh?

Very nicely done.

Now, what is the difference between the 18650 and 21700 cells? Size? Reliability? I'm wondering which I need to see about getting to make my own battery packs.

Thanks.

Steve

You wouldn't be interested in selling end cap sets?

Hi Dave,  Mr. National Intermediate Champion!!! (hey buddy you earned it and you have bragging rights for about 7 more months!)

NICE WORK! Thanks for sharing your methodical approach to assure you have good solder joints.  Also like the end caps,  I also have a lot of airplanes that could use the 2700's - it is a good size.

The way you made that pack makes me wonder if a 4 across "flat pack" would be viable?  Imagine a pack that could be mounted internally in a profile fuse?  Also looks like a 2x3 cell layout would be a completely viable 6S layout

Question for you and the other Li-Ion pioneers:  Are there suitable cells available around 1800-2200 range?  More important, would they offer important savings in size & weight?  Historically i have used 4Sx2200's in many airplanes.  I have also been driving down the battery sizes on several airplanes, for example using 4Sx1800 (175g/6.2 oz) in the Stuka Stunt and 4Sx1300's (4.8 oz) in the Barnstormer. Li-Ions would seem to offer potential further size & weight savings in smaller packs that they do in the larger sizes.

THANKS in advance

3D printed available in limited qty.
See:  https://stunthanger.com/smf/classifieds-92/4s-li-ion-2x2-3d-printed-parts/

Dan,
Was he as good looking as I am?  You only have 2 choices then!!!

I saw a guy this summer at my local flying field who had a pack just like this. Amazing ! Hey you're from Ohio. So was this guy.