This page was machine-translated from German. German original version
Battery repair, cell replacement and custom-built battery packs
We repair your defective battery by replacing all cells with new ones. We use branded cells, for example from LG and Murata (formerly Sony), and tell you exactly which cells and how many of them we fit.
Our services
We fit battery packs with nickel or lithium-ion cells – for example for e-bikes, electric mopeds, scooters, power tools and household appliances. We are happy to clarify in advance whether your model is possible.
Cell replacement
All cells are replaced. We continue to use the housing, connections and electronics as long as they are in good order. The configuration and electronics must match the original battery.
More capacity
On request, we fit cells with a higher capacity. The number and arrangement of the cells remain the same, because the space in the housing is limited. Whether an upgrade is possible depends on the available cells, the BMS, the motor and the charger – we check this and discuss it with you beforehand.
Estimate an upgradeCustom-built battery packs
On request, we also make battery packs to measure, for example for unusual housings or cell arrangements. When needed, we design suitable cell holders ourselves and produce them by 3D printing. What is possible is clarified individually with you.
How cell replacement works
The scope of the work and tests depends on the existing battery and the agreed order.
Testing and measuring
A battery consists of several cell groups connected in series. The voltages of the individual groups give indications of its condition: if one group deviates significantly, it is often the cause of shutdowns or low range. We then discuss with you whether a repair is worthwhile and what it will cost.
Opening and recording
Before disassembly, we record the configuration (for example 10S4P: 10 groups in series, each with 4 cells in parallel), the position of the cells, the battery management system (BMS) with its sensing wires, temperature sensors, switches and connections.
Selecting suitable cells
The format, capacity and current rating of the cells must match the device, motor and charger. The specific cell used is stated in the order.[1]
Measuring and sorting
New cells also vary slightly. Cells can be put together into groups with a similar total capacity. This is important because the weakest group limits the whole battery: the BMS stops discharging as soon as that group reaches its minimum voltage.[2]
Arrangement and cell holders
Cell holders secure the cells in the housing. When needed, we design suitable holders and produce them by 3D printing. With cell replacement, the arrangement must match the existing battery.
Spot welding instead of soldering
The cells are connected with nickel strips – using a pulse spot welder that Fernand Heinen built himself and designed himself, starting from the circuit board. Cell manufacturers such as Panasonic specify that cells must not be soldered directly – too much heat can damage the cell.[3] Research also specifically examines the heat input when connecting cells.[4]
Connecting the BMS and insulating
The battery management system monitors the voltage of each cell group as well as temperature and current, and switches off when limit values are reached.[2][5] The terminals are insulated against short circuits, and wires are given strain relief.
Exact details of the cells
The order states the cell type, number and configuration. Using the cell manufacturer’s data, you can recalculate the capacity yourself – for example 10S4P with cells of 3.7 V and 2.5 Ah: 37 V × 10 Ah = 370 Wh. Go to the battery calculator
What matters with cells
From the outside, cells often look the same. The difference lies inside – and it can be measured.
Built-in protective elements
Many branded cells contain internal protective components, for example against overpressure or overcharging (CID) and – depending on the type – against overcurrent (PTC).[6] In investigations by UL, these were missing in counterfeit cells.[7]
Verifiable capacity
Counterfeit cells often carry ratings they do not achieve: UL documents a cell labelled 5,000 mAh with a measured 1,200 mAh.[7] According to the manufacturer, a branded cell such as the LG MJ1 has 3,500 mAh.[1]
Careful workmanship
Measuring and sorting the cells and spot welding according to the manufacturer’s specifications[3] take time and measuring equipment. However, they are important for service life and safety. In a CT examination of 1,054 cells, all 33 cells with serious manufacturing defects came from low-cost or counterfeit brands.[8]
Frequently asked questions
Which batteries can you repair?
We fit existing battery packs with new nickel or lithium-ion cells – for example for e-bikes, electric mopeds, scooters, power tools and household appliances. We are happy to clarify in advance whether your model is possible. You will find examples under Battery examples.
Do you also make new battery packs?
Yes, on request as custom-built battery packs, for example for unusual housings or cell arrangements. Write to us and tell us what you need the battery for and what dimensions and values it should have.
Can I repair my battery myself?
We advise against it. The German Social Accident Insurance (DGUV) warns that batteries should not be opened, tampered with or modified, because this destroys protective devices and there is a risk of heat generation, ignition or explosion.[9] If you would like to have new cells fitted in your battery, this belongs in a workshop with suitable equipment – in our case, for example, with a pulse spot welder instead of a soldering iron. More on this under Care and safety.
Can the capacity be increased?
On request, we fit cells with a higher capacity. The number and arrangement of the cells remain the same. Whether an upgrade is possible depends on the available cells, the BMS, the motor and the charger – we discuss this with you beforehand.
What rights do I have in the event of defects?
The statutory warranty applies: we are liable for the new parts fitted and for our work for two years from the return of the battery; we remedy a defect free of charge. We do not offer an additional voluntary guarantee; guarantee commitments already given remain unaffected. Details under Statutory warranty. If anything is not in order after the repair, please contact us directly.
What does the price depend on?
Mainly on the number and type of cells your battery needs and on the effort involved in opening, connecting and insulating. On the basis of your photos, we give you a non-binding assessment; we state the binding price before we begin. You can read why branded cells make the difference under What matters with cells.
Can I send in my battery?
Please contact us beforehand. Lithium batteries are dangerous goods for shipping – up to 100 Wh with simplified rules, above that the full regulations apply; we will discuss with you how the battery can reach us safely. Please do not ship damaged or swollen batteries. You will find the costs under Shipping and payment.
Which countries do you ship batteries back to?
To Luxembourg, Germany, France, Belgium, the Netherlands, Austria, Italy, Spain and Portugal. Lithium batteries above 100 Wh, such as most e-bike batteries, are subject to the full dangerous goods regulations; we agree the shipping with you in advance. More under Shipping and payment.
What information helps with a request?
A photo of the battery and its rating plate, the manufacturer and model of the device and a short description of the problem.
Sources (9)
- Manufacturer data for the cells: LG (INR18650-MJ1, -M29, -M26/M26S, INR18650-HE2), Sony/Murata (US18650VTC4, VTC5, VTC6), Panasonic NCR18650PF and Axcom Sub-C (YT2000SCP, YT3000SCP), as technical examples; Molicel INR21700-P45B; Samsung INR21700-50E; Lithium Werks ANR26650M1B; LiFePO4 cell IFR32700 (retailer data). Link
- Fraunhofer IIS: Batteriemanagementsysteme [Battery management systems] (product sheet). Link
- Panasonic: specification of the NCR18650B lithium-ion cell (“Do not directly solder to the battery”, connection by spot welding) and Sanyo/Panasonic Safety Data Sheet SDS-IBT-00026 (2018). Link
- M. J. Brand, P. A. Schmidt, M. F. Zaeh, A. Jossen: Welding techniques for battery cells and resulting electrical contact resistances. Journal of Energy Storage 1 (2015) 7–14. doi:10.1016/j.est.2015.04.001 Link
- VDE (German Association for Electrical, Electronic and Information Technologies): FAQ Batterien [FAQ on batteries]. Link
- J. Jeevarajan: Limitations of Internal Protective Devices in High-Voltage/High-Capacity Batteries Using Lithium-Ion Cylindrical Commercial Cells. NASA NESC Technical Bulletin 09-02, 2009. Link
- UL (Underwriters Laboratories): Counterfeit Batteries eGuide. Link
- Lumafield: Battery Quality Report – CT analysis of 1,054 cells in 18650 format (2025). Link
- Deutsche Gesetzliche Unfallversicherung (DGUV, German Social Accident Insurance): DGUV Information 205-041 “Brandschutz beim Umgang mit Lithium-Ionen-Batterien” [Fire protection when handling lithium-ion batteries], edition February 2024, sections 4.2 (p. 20: heat input during contacting) and 4.3 (p. 23: do not tamper with or “repair” the battery). Link
Show us your battery
A photo of the battery and its rating plate and a short description of the fault are enough for an initial assessment.