Hailong vs Silver Fish battery case — which one fits your build?

Short answer: choose by how the case mounts, not by how many cells it holds. A Hailong case hangs on a bracket and engages from the side. A Silver Fish — sold elsewhere as "rear plug-in" — slides into a channel from the rear. The two overlap almost completely on cell count, so picking between them on capacity alone is solving the wrong problem.

The two names get treated as rivals because they show up next to each other in every catalogue. They are not two sizes of the same thing. They are two mounting systems, and they assume different things about your frame.

The one place they genuinely separate is the longest pack each can take. The longest opening in our Silver Fish range is 530 mm against 396 mm for Hailong. If you are building a big-capacity pack in a single long row — the kind that needs more than 117 cells of 18650 or 100 on 21700 — that length is what decides it, and on that measure only one of the two formats will do.

Where they do not separate is capacity. This is the part buyers get wrong. The Hailong range reaches 117 cells of 18650 and 100 of 21700; Silver Fish reaches 130 and 160. Those bands overlap across almost their whole length — a mid-size build could be housed by either format, and the deciding factor is the frame, not the number. Anyone who tells you to "pick the bigger format" is answering a question you did not ask.

Pick a Hailong when:

• your frame has a flat mounting face, or already carries a Hailong bracket — it is the most standardised pattern there is, so brackets, locks and spare cases are easy to find;
• you want the fewest unknowns. 15 moulds cover 117 cells of 18650 and 100 of 21700, which is enough range for a normal 36–52 V build;
• you want to service the pack without unbolting anything behind the seat tube.

Pick a Silver Fish when:

• you need a long, narrow housing — the longest one we mould takes 130 cells of 18650, which nothing in the Hailong range reaches;
• the space you have is a channel behind the seat tube or a rail along a rack, where a long tube fits and a box does not;
• you are building on 21700 at the top of the range: 160 cells against 100.

The mistake worth avoiding. Builders sometimes pick Silver Fish assuming it is "the bigger one", then find the mounting channel does not exist on their frame. The length advantage is real, but it only helps if the frame has somewhere to put a tube that long. Measure the mounting area first, then choose the format — not the other way round.

Once you know which format your frame takes, the case selector narrows it to the specific moulds that accept your cell count and configuration, with the opening length for each. Both series are listed in full — all 15 Hailong and all 27 Silver Fish moulds — on the Hailong and Silver Fish pages.