5-pin, 3-pin or XLR: what a battery case connector actually changes

Short answer: on our housings the connector is a part-level choice, not a mould-level one. The port is cut into an end cap or an end land that sits outside the length figure you order, which is why 3-pin, 5-pin and XLR can ride on the same mould. What does force a new mould is the interface on the frame side of the battery — the dock the housing plugs into — and that is fixed by the housing section, not by the plug.

Buyers arrive here with one question that is really two: "will your housing take my connector" and "will it fit my frame". The first usually costs nothing and adds no lead time. The second is the one that costs a tool.

Where the port physically sits

Every housing has a body whose length is the figure you order, and end regions outside it. That figure is not the same measurement in both families: on a downtube drawing it is L2, the internal opening the pack sits in; on a Silver Fish drawing it is L, the aluminium tube length. Outside it sit the end cap, the connector block and the cable exit — and those are what a port is cut into.

On the five drawings we worked from for this page, the two ends are never equal and the allowance ranges from 7.2 mm to 57.5 mm:

Three things follow, and between them they answer most of the connector mail we get.

The port does not cost cells. It is cut in the end allowance, outside L2 or L, so specifying a 5-pin instead of a 3-pin does not move the cell ceiling by one. What does sit inside the ordered length is the BMS, above or beside the cell block, and a 20S board is longer than the 10S board these moulds were drawn around. That is a different problem, worked through in why your 13S5P pack will not fit.

Ordered length is not part length. A 325 mm Silver Fish tube with 32.85 mm at one end and 7.2 mm at the other is a 365 mm part. If you are checking a housing against a window in the frame, use the sum. ALX080 is the other extreme: 57.5 mm and 35 mm, 92.5 mm of housing outside the tube.

The two ends are not interchangeable. On ALX035B and ALX040 one end is 7.2–7.3 mm and the other 32.85 mm, so a connector with a long boot or a right-angled exit has to be checked against the end it will actually sit on. That is a drawing question, and it is cheaper before the order than after.

What is standard on our range

Across the Silver Fish range — 23 moulds — most housings are bottom-wired, and each of those can be built with either a 3-pin or a 5-pin connector. That is a catalogue choice, not a modification: no new mould, no tooling charge. A 3-pin XLR charging inlet is routine for us too, and on a bottom-wired housing the usual arrangement is the discharge port at the bottom end and the charging inlet in the opposite cap.

Two things are fixed at the order and worth settling in writing: which end each port sits on, and whether charge and discharge share an end. Both arrangements are possible, and they produce different end caps — the difference only becomes visible when the drawing is issued.

Who supplies the connector. Either side. We can buy the connector and fit it, or you send the connector and we cut the pocket to it. If you send it, send the mating connector's part number or a clear photo of its mating face: the pinout and the keyway belong to the plug, and a drawing that says "5-pin" without a part number is not enough to cut a pocket that lines up on the first try.

36 V, 15 Ah and 20 Ah in a Silver Fish housing

This is the pair that arrives together most often, and once the port is settled the cell count is what picks the housing.

On 18650 both packs clear the 65-cell housings without argument. 15 Ah is 10S5P on 3.0 Ah cells (50 cells); 20 Ah is 10S5P on 4.0 Ah or 10S6P on 3.5 Ah (50 to 60 cells).

On 21700 it is tighter, and this is where a housing gets ordered one size too small. 20 Ah on 5 Ah 21700 cells is 10S4P — 40 cells. ALX080 tops out at 39 on 21700 at either tube length, so it is one cell short of that pack, at any length. ALX035B reaches 52, but only from 325 mm; the 285 mm version is 39. Same model number, same connector, one cell between "fits" and "does not".

When the connector really is a mould question

Not the plug — the interface. A frame battery that docks into a recess in the down tube is held by a module moulded into the housing: the pocket, the rails, the latch. That module is dimensioned by the housing section, and our two downtube sections are 74.5 × 108 mm (ALX030) and 67.9 × 86.1 mm (ALX058). If the recess you are matching is a 65–80 mm class envelope, no standard downtube housing enters it whatever connector it carries. That is a new tool, and no choice of plug changes it.

One more boundary worth knowing before a drawing is approved: a port cut into an end cap changes the cap, and nothing else. A port through the side of the main body is either a change to the tool or a second operation after moulding — ask which, and ask for both prices, because the two differ by an order of magnitude and the answer is model-specific.

What to send with the enquiry

• The mating connector's part number, or a photo of its mating face.
• Which end each port sits on, and whether charge and discharge share an end.
• Who supplies the connector — you or us.
• The length figure, the cell format and the pack configuration. Say whether the length you are quoting is L2 (downtube, internal opening) or L (Silver Fish, tube length) — two different measurements that both get written as "325 mm" in an email.

The measured size table carries the opening and the section for all 90 models, and the Silver Fish series page lists every tube length against both cell ceilings. A question like "which of these takes 40 cells of 21700 at 325 mm with my connector" is answered from those three numbers — no sample needed.