KT-S01 — 36V Seatpost Battery, Ø53mm Tube
The concealed option for lightweight and urban bikes: 5Ah in a 410mm post or 7.5Ah in a 610mm post, with the pack inside the seat tube.
Key Details
- MOQ
- From 100 pcs
- Sample Lead Time
- 5–10 working days
- Mass Production
- 2–4 weeks after approval
- Voltage
- 36V
- Capacity Range
- 5–7.5Ah
- Form Factor
- Seatpost / in-tube
Cell Brands
The KT-S01 hides the battery inside the seat tube. That is the entire proposition: no visible pack, no down-tube bracket, a bike that reads as unpowered. It is a Ø53mm tube carrying 18650 cells in a moulded holder, available in two lengths — 410mm for a 20-cell 10S2P build at 36V 5Ah, or 610mm for a 30-cell 10S3P build at 36V 7.5Ah.
The trade is honest and worth stating plainly: this format holds a fraction of what a down-tube or integrated pack holds. Seven and a half amp-hours at 36V is about 270Wh, against 1,200Wh or more from the KT-E09. Specify a seatpost battery when concealment and weight are the product, not when range is.
Fit is set by usable tube depth, not tube length
The number that decides between the 410mm and 610mm build is how deep the seat tube runs clear before it meets the bottom bracket shell or a bend. Measure that, not the exposed post length. Getting this wrong is the usual reason a seatpost programme goes back for a second sample.
Cell holder bores are Ø18.5mm, so this platform is 18650-only. If the programme needs 21700 cells — and the capacity that comes with them — the KT-S02 takes a 21700 holder and reaches 15Ah in a 610mm post.
Tail light, discharge position, and the clamp
Two options are worth deciding early because both are tooling: an integrated tail light in the post head, and a bottom-discharge outlet that brings the harness out of the lower end rather than the top. Bottom discharge is what lets the wiring stay inside the frame, which is usually why a brand chose a concealed battery in the first place.
Clamp hardware is available plain or lockable, with moulded end caps. CE, UN 38.3 and IEC 62133 documentation is issued against the configuration ordered — and at 180–270Wh these packs sit well above the 100Wh air-freight exemption, so the transport paperwork is the same regime as a full-size pack. See shipping lithium e-bike batteries.
Technical Specifications
| Enclosure Format | Seatpost / in-tube (concealed) |
|---|---|
| Tube Diameter | Ø53.0 mm outer · Ø18.5 mm cell holder bores |
| 410 mm Length | 20 cells · 10S2P · 36V 5Ah |
| 610 mm Length | 30 cells · 10S3P · 36V 7.5Ah |
| Cell Format | 18650 |
| Options | Integrated tail light · bottom-discharge outlet |
| BMS | In-house 10S BMS sized to the 2P / 3P arrangement |
| Mounting | Seat-tube clamp; lockable clamp and moulded end caps available |
| Connector | Specified per programme |
| MOQ | From 100 pcs |
| Sample Lead Time | 5–10 working days |
| Mass Production | 2–4 weeks after approval |
Inside Every Pack
The same engineering standards apply to every configuration we ship — from cell selection to the final welded enclosure.
Tier-1 Brand Cells
Samsung, LG, Panasonic, EVE and BAK cells — graded and capacity-matched before assembly.
Multi-Protection BMS
Over-charge, over-discharge, short-circuit and temperature protection on every pack.
Welded Construction
Nickel strips welded for low-resistance, vibration-resistant joints inside a sealed enclosure.
Applications
Certifications Included
Test reports and certificates are included in shipment documentation at no additional cost.
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From 100 pcs · Samples in 5–10 working days · Mass production 2–4 weeks after approval
Frequently Asked Questions
How much range does 5Ah at 36V actually give?
About 180Wh, which on a light bike with a 250W hub motor and pedal assist is typically 25–35km depending on rider weight, terrain and assist level. This is a lightweight-bike and range-extender platform, not a touring one.
Does the seat tube need to be exactly Ø53mm?
The pack body is Ø53mm outer, so the tube's inner diameter has to clear that with fitting tolerance. Send the seat tube's internal diameter and usable depth — the usable depth, not the tube length, is what sets whether you get the 410mm or the 610mm build.
What does the bottom-discharge option change?
It moves the output from the head of the post to the lower end, so the harness can be routed inside the frame instead of over the saddle clamp. On a concealed-battery bike that is usually the point of choosing this format at all.
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