Solved Stacking several smaller LiPo batteries or finding the perfect sized one?

[RoseDagger]

So I discovered in my work log/contest entry that I won't be able to fit the regular 18650 batteries I had planned, and started looking at LiPo batteries.
While looking at eBay for batteries in all different sizes I started wondering whether it would be better to stack multiple smaller batteries to fill the space I have, or try to find one big one that fills the allotted amount of space?

Say I have about 64mm/70mm/9mm of space (These are not exact and there are some wiggle room)
What I have found so far is:
I can stack four 422770 1100mAh, two in height and two in width, to get a battery pack of 4400mAh 54mm/70mm/8.2mm (The margins are rather thin, and I would have to remeasure before I order, but I think I could make it work, and it is there closest I have gotten to the specs and the highest capacity)
Or say two 503450 1000mAh giving me 64/50/5 2000mAh
Edit: found a better 2x: 335865 1800mAh, stacked in height for 58mm/65mm/6.6mm 3600mAh /edit
Or one 605068 2500mAh for 50mm/68mm/6mm
Larger batteries seem to either jump up to 10mm height or 80mm length, which is both outside my specs.

It seems like I can get higher capacity and more easily fill the volume by stacking multiple smaller batteries, as there seems to be higher demand and choice in that size class, then when trying to find the perfect-sized battery. But are there downsides to doing that? Like the batteries getting hotter and more explody? stacked sizes being larger than anticipated? or other concerns?

Edit2:
Found a 3x one. 306062 1800mAh, stacked three in height for 60mm/62mm/9mm at 5600mAh. And if I can't fit it height wise, I can still run it as a 2x one with a height of only 6mm.
Which seems like a safer solution than banking on the 4x one where it is at the limits in two directions. Though the question still stands, with my best option so far being a triple layer battery, with one of the batteries being sandwiched between two other ones, is there any downsides or risks, to where trying to aim for just one perfectly sized battery would be preferable?

(also was not sure if this counted more under modding 101, or general, or somewhere else, as I did not see a battery-specific section else where)

 

[cheese]

I'll start with the explody part first... It's completely fine to stack cells as long as they are combine into a pack before being used. All brand new cells are perfectly fine, just don't combine used ones into new packs. This is because the different capacities of the cells will cause them to charge each other as they are being used which makes them hot.

The only real downside I know of is that it's a bit harder to wire since you'll need to connect all the batteries together. As long as they're wired correctly and you aren't crushing any wires/batteries you're fine

 

[RoseDagger]

I'll start with the explody part first... It's completely fine to stack cells as long as they are combine into a pack before being used. All brand new cells are perfectly fine, just don't combine used ones into new packs. This is because the different capacities of the cells will cause them to charge each other as they are being used which makes them hot.

The only real downside I know of is that it's a bit harder to wire since you'll need to connect all the batteries together. As long as they're wired correctly and you aren't crushing any wires/batteries you're fine

Thanks, that is really reassuring to know. I'll just continue using my 18650 battery as a test battery until I'm ready to install all the LiPos as a single battery pack and be careful of the wiring.

 

[Shank]

You can stack multiple cells together, just make sure they are new cells, like Cheese suggested. When using multiple cells, it is important to make sure they are the same capacity, and cycle count.