The most common reason a triangle battery does not fit is not the headline dimensions. It is clearance: the straps, the cable bend radius, the connector body, and the path you need to lift the pack out again. Measuring takes about five minutes and it is the cheapest thing you can do before ordering.
What you need
- A steel tape measure or ruler.
- Cardboard and a marker, or a piece of string.
- A phone camera.
The four measurements that matter
- Length along the down tube. Measure from the head tube or the point where the down tube meets the bottom bracket area, along the tube, to where the triangle narrows. Write down the longest usable run, not the widest point.
- Height along the seat tube. Measure from the top of the down-tube junction up to the point where the triangle closes, usually where the top tube or the seat post clamp sits.
- Width at the widest usable point. Triangle cases are wedge shaped, so the width you can use depends on where in the triangle the pack sits. Measure at the point where the pack will actually be, not at the frame's widest.
- The removal path. This is the one people skip. The pack has to come out for charging and servicing. Check that it clears the top tube, the seat post and any bottle cage bosses on the way out.
Then build a template
Cut cardboard to the listed dimensions of the pack you want and tape it into the triangle. Do not just eyeball it. The template shows you in ten seconds what the spec sheet cannot: whether the connector hits the seat tube, whether the cable has room to bend, and whether you can still get your hand around the pack to lift it.
Clearance to allow for
- Cables and connectors. Discharge connectors are bulky and the cable needs a bend radius. Allow real space at the end of the pack where the lead exits.
- Straps or mounting hardware. Add the thickness of whatever holds the pack in.
- Crank and front derailleur. Check that the pack does not foul the crank at the bottom of the triangle, or any cable run on the seat tube.
- Bottle cage bosses. These protrude and are a common reason a pack that measures fine on paper will not sit flat.
Send us this and we will confirm fit
Before you order, take four photos and note three numbers:
- a side-on photo of the whole frame triangle with the tape measure visible;
- a close-up of where the connector and cables would sit;
- a photo of your controller label, so we can confirm voltage and current;
- a photo of your current battery connector, if you have one;
- and the length, height and width numbers you measured above.
Send those with the pack you are considering and we will tell you whether it fits before you pay. This matters more than usual here: we do not accept returns, so a five-minute check now is worth a lot more than a return request later. See the e-bike battery collection for the packs currently listed, our voltage comparison guide if you have not picked a voltage yet, and the warranty page for what is and is not covered.