Water bottle e-bike battery case — how many cells actually fit
Short answer: a water-bottle housing is the smallest format we mould, and it still takes 52 cells of 18650 — enough for a 13S4P 48 V pack. What it is not is a route to a big-capacity build: that ceiling is about a quarter of what the largest downtube housing takes.
Short answer: a water-bottle housing is the smallest format we mould, and it still takes 52 cells of 18650 — enough for a 13S4P 48 V pack. What it is not is a route to a big-capacity build: that ceiling is about a quarter of what the largest downtube housing takes.
The bottle-boss position is the one place on a bike that is already engineered to carry something. It has mounting points, it is out of the way of the cranks, and nothing about the bike has to change to use it. The cost is volume — a bottle-shaped housing holds far less than a tube-shaped one, and that is the whole trade.
| Water bottle | Downtube (for scale) | |
|---|---|---|
| Housings we mould | 2 | 21 |
| 18650 ceiling | 52 cells | 200 cells |
| 21700 ceiling | 20 cells | 160 cells |
| Longest opening we mould | 319 mm | 538 mm |
52 cells is more than it sounds. A 52-cell pack wired 13S4P is a 48 V battery with four cells in parallel per group — a normal commuter pack, not a range extender. Builders who dismiss the bottle position as "only good for a small battery" are usually comparing it against a downtube housing, which is a different job entirely.
What a bottle housing does not do: scale. Our largest bottle housing tops out at 52 cells of 18650 and 20 of 21700. If your target pack is bigger than that, no amount of shopping will fix it — you need a tube format (downtube or one of the in-frame housings), where the ceiling is several times higher. The 319 mm longest opening is the physical reason: there is only so much length in a bottle.
Where it wins. Three cases where the bottle position beats everything else:
- The frame triangle is small or curved. Step-through frames, folding bikes and small-wheel bikes often have no flat face long enough for a tube housing. The bottle bosses are still there.
- You want the bike to look like a bike. A bottle housing reads as a water bottle at a glance. On a commuter locked up on a street, that is worth something.
- You are building a second, smaller pack. Two independent packs (one for the daily commute, one for a long weekend ride) sometimes make more sense than one big one, and the bottle position is free space.
Both bottle housings we mould are listed with their cell ceilings and opening lengths on the water bottle page. If you are still working out which format your frame can take, start with the case selector.
Common questions
How many cells fit in a water bottle battery case?
Can a water bottle battery power a full-size e-bike?
Why are bottle housings so much smaller than downtube ones?
Is the water bottle position strong enough?
Send us the pack and we will confirm the fit
Cell type, series and parallel count is usually enough. If the answer is that none of our moulds fit, we will say so rather than sell you the nearest thing.