DAHON Seatpost Battery Rebuild: Upgrading the Unio E20 & K-One 36V Battery to 10.5Ah

A New Rebuild Option for DAHON Electric Bike Owners

One of the more interesting batteries to arrive at E-Bike Marketplace recently is the long, integrated DAHON 36V seatpost battery used on compatible DAHON Unio E20 and K-One electric bicycles.

Instead of mounting a conventional battery on the downtube or rear rack, DAHON integrates the battery into a cylindrical seatpost assembly. It's an elegant solution—but when the lithium-ion cells eventually age, replacing the entire assembly can become expensive.

DAHON currently lists its 57mm Unio E20 and K-One seatpost battery at 36V 9.5Ah, with a current sale price of $599 and regular price of $699.

That's exactly the kind of battery where rebuilding can make sense.

We Now Have One in Our Battery Lab

We currently have an original DAHON seatpost battery in our facility for evaluation and rebuilding.

Rather than throwing away a perfectly usable enclosure, mounting system and other serviceable components, our approach is to carefully open the assembly and replace the aging lithium-ion cell group.

Based on the available space and expected internal configuration, we're targeting an upgraded specification of:

36V 10.5Ah – approximately 378Wh

Once the battery is opened, we'll document its exact original cell configuration and internal construction.

From 9.5Ah to 10.5Ah

The factory 57mm DAHON battery is specified at 9.5Ah. Our planned 10.5Ah rebuild represents approximately a 10% increase in rated capacity.

That doesn't require changing the external dimensions of the seatpost. The additional capacity comes from using modern, higher-capacity lithium-ion cells inside the original enclosure.

The goal is simple: keep the DAHON design, replace what has aged, and improve the internal battery where the original architecture allows it.

Why Rebuild Instead of Replace?

An e-bike battery is much more than its lithium-ion cells.

The DAHON seatpost assembly incorporates the physical enclosure, mounting hardware, electrical connections and battery electronics into a very specific package designed to fit the bicycle.

When those components remain serviceable, replacing the complete assembly isn't always necessary.

During a rebuild, we can retain compatible original hardware while replacing the component that experiences the greatest age-related degradation: the lithium-ion cell pack itself.

Our DAHON Rebuild Will Be $549

We're introducing the DAHON 57mm Seatpost Battery Rebuild for $549 plus return shipping.

The service includes disassembly, inspection, replacement of the aging lithium-ion cell group, rebuilding of the internal pack, reassembly and final battery testing.

For compatible batteries, we're targeting an upgrade from the original 36V 9.5Ah specification to approximately 36V 10.5Ah.

What Happens to the Original Battery?

You send us your existing DAHON battery.

Our battery technicians inspect the enclosure and electronics before beginning the rebuild. The original aging cells are removed and replaced with a new matched set of 18650 lithium-ion cells.

Whenever serviceable, we retain the original:

• Seatpost enclosure
• Mounting components
• Connectors
• Wiring
• Battery electronics
• External appearance

Once assembled, the battery goes through charge, discharge and protection testing before being approved for return.

57mm vs. 53mm DAHON Batteries

There's one important compatibility detail DAHON owners need to know.

DAHON states that some K-One bicycles use a 53mm seatpost battery instead of the 57mm version.

Before ordering a rebuild, verify which version you have. If you're unsure, send E-Bike Marketplace photographs of the battery, its label and connector and we can help identify it.

Don't Throw Away an Original Battery Just Because the Cells Are Old

Specialized e-bike batteries like this are exactly why E-Bike Marketplace continues investing in battery rebuilding.

As electric bicycles age, complete replacement batteries can become expensive, difficult to locate or eventually discontinued. In many cases, however, the enclosure and hardware are still perfectly usable.

Rebuilding gives us an opportunity to preserve that original equipment while installing a fresh internal energy-storage system.

If you own a DAHON Unio E20, K-One or another DAHON electric bicycle with a seatpost battery, contact E-Bike Marketplace. Even if your exact battery isn't listed on our website yet, our battery team can evaluate it for rebuilding.

E-Bike Marketplace is an independent battery rebuilding company and is not affiliated with or endorsed by DAHON. Product and model names are used for compatibility identification.