E-bike battery cases for 21700 cell builds
A case listed as "18650 or 21700 compatible" holds noticeably fewer cells on 21700, and the gulf is wider than most listings admit.
Who this is for: Assemblers who have standardised on 21700 and need the housing envelope to match.
What this build actually constrains
Same mould, fewer cells
A 21700 is fatter. A housing that takes 91 cells on 18650 typically takes around 70 on 21700 — the difference is not a rounding error.
Check both numbers, not the bigger one
Listings quote the 18650 figure because it is larger. If you are building on 21700 that number is not about your build.
High-current builds want space between cells
More current means more heat. Packing a 21700 pack to the absolute maximum leaves no room for that.
What we would put on this build
- ['
- Silver Fish — 27 models, up to 130 cells on 18650 and 160 on 21700. ', '
- Downtube — 21 models, up to 200 cells on 18650 and 160 on 21700. ', '
- Rear Rack — 17 models, up to 104 cells on 18650 and 78 on 21700. ']
Water Bottle
The bottle format's 21700 ceiling is the lowest in the whole range. If your build is 21700 and capacity matters, this format will not get you there.
Models worth starting from
Full range in every format, with the numbers, in the format comparison.
Questions we get about this build
How many 21700 cells fit in a Hailong case?
Is 21700 better than 18650 for an e-bike?
Send us the build and we will say which format works
Frame envelope, cell type, series and parallel count is all we need. If the answer is that none of our moulds fit and it needs a new one, we will say that rather than sell you the nearest thing.