Battery repair and replacement
We repair your defective battery by replacing all cells with new cells. We can also increase capacity upon request. We use branded cells, for example from LG and Sony, and tell you exactly which cells and how many of them we use.
From the tired battery
to the new cell package.
The graphics explain the technical basics of new equipment. They are schematic examples; The work on your existing battery will be arranged individually.
Check: What is the problem?
A battery consists of several groups of cells connected in series. The tensions of the individual groups can provide clues about the condition. If a group deviates significantly, it is often the cause of shutdowns or low range.
We will then discuss with you whether a repair is worthwhile and how much it will cost.
Press “Measure” (example values).
Open and hold
When re-equipping, the existing structure is taken into account. Wiring, connections and electronics must match the original battery.
We continue to use housings, connections and electronics as long as they are in order.
- Interconnection – for example 10S4P: 10 groups in series, 4 cells in parallel each
- Location of the cells and space in the housing
- Battery management (BMS) and its measuring lines
- Temperature sensor, switches and displays
- Connections and plugs
Choose the appropriate cell
The format, capacity and load capacity of the cells must match the device, motor and charger. We use branded cells, for example from LG and Sony. The selection depends on the existing battery.
More capacity: If requested, we can use cells with higher capacity – if the electronics and charger allow it.
Technical examples of cell types; The specific cell used is specified in the order.[8]
Measure and sort
New cells also scatter easily. The graphic shows an example of how cells can be put together into groups with similar total capacity. It does not describe a promised single cell measurement.
This is important because the weakest group limits the entire battery: the BMS stops discharging as soon as the weakest group reaches its minimum voltage.[4]
Arrangement and cell holder
Cell holders fix the cells in the existing housing. The example shows a grid; it is not an offer to design new battery packs or cell holders.
Not every existing battery uses cell holders. Staggered arrangements can save space. When re-equipping, the arrangement must match the existing battery.
Spot welding instead of soldering
The cells are connected via nickel strips. The following applies to pulse spot welding: two electrodes press on the strip and a very short, strong current pulse connects it to the cell pole in a point-like manner.
Cell manufacturers such as Panasonic stipulate that cells should not be soldered directly, but rather connected using spot welding - too much heat can damage the cell.[6] Researchers are also specifically examining the heat input when connecting cells.[7]
Simplified representation of the heat load on the cell (qualitative, not to scale).
Connect and isolate BMS
The battery management system (BMS) monitors the voltage of each cell group as well as temperature and current and switches off at limit values.[4][1] The schematic representation shows measuring lines and insulation. Which functions the existing BMS supports depends on the battery model.
- Insulation on the poles against short circuits
- Heat-resistant insulating tape and shrink tubing
- Strain relief for the cables
Test and precise information
The scope of work and testing depends on the existing battery and the agreed order.
We will tell you exactly which cells and how many of them we use. So you don't just have to believe the capacity information: you can use the cell manufacturer's information to calculate the capacity yourself.
10S → 10 × 3.7V = 37V
4P → 4 × 2.5 Ah = 10 Ah
Energy: 37V × 10Ah = 370Wh
Why a good battery?
has its price.
Cheap replacement batteries and cells without brand identification often look the same from the outside. The difference is inside – and it is measurable.
Traceable capacity
We will tell you exactly which cells and how many of them we use. You can calculate the capacity yourself using the manufacturer's information.
Measured, sorted, spot welded
Measuring and sorting the cells and spot welding according to manufacturer specifications[6] cost time and measurement technology - but they are important for service life and safety.
Personally available – even afterwards
You will receive an invoice, and even after the repair we will be there to answer your questions personally if you have any questions.
Imprint or measured value?
Fake cells often carry information that is beyond their reach. Two documented examples:
UL, “Counterfeit Batteries eGuide.”[9] Lumafield, “Battery Quality Report” (2025): CT examination of 1,054 cells in 18650 format; All 33 cells with serious manufacturing defects came from cheap or counterfeit brands.[11] LG MJ1 according to the manufacturer's information.[8]
✓ CID against overpressure
✓ Manufacturer's data sheet
✗ CID was missing
✗ Fire in the overload test
Structure and capacity
recalculate.
For existing lithium-ion batteries with 18650 or 21700 cells. Volts and Ah alone do not clearly indicate the number of cells. The calculator shows suitable example calculations.
Rated voltage: 3.6-3.7V per cell; Charging limit: 4.2 V per cell. Only for these lithium-ion examples, not for nickel or LiFePO4 batteries. Market designations such as “48 V” are rounded. The cell type and wiring of the actual battery are binding.
Answered briefly.
Is your question not included? Call us or write to us – we will advise you personally.
Ask a question →Which batteries can you repair?
We equip existing battery packs with nickel or lithium-ion cells - for example for e-bikes, e-scooters, scooters, tools, household appliances and much more. We would be happy to clarify in advance whether your model is possible.
Can the capacity be increased?
If requested, we use cells with 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, BMS, motor and charger - we will discuss this with you in advance.
What rights do I have in the event of defects?
The statutory warranty rights apply. We do not promise any additional voluntary guarantee for new orders. Guarantees that have already been issued remain unaffected. If something is wrong after the repair, please contact us directly.
Why does a new battery cost more than a cheap replacement battery?
We use branded cells from LG and Sony and specify the cell type and circuitry. The exact scope of the new equipment will be agreed for your existing battery. Find out more in the “Quality & Price” section on this page.
Can I send in my battery?
Please contact us beforehand. Lithium batteries are considered dangerous goods when shipped; We will discuss with you how the battery gets to us safely. Please do not send damaged or bloated batteries.
What information will help with the request?
A photo of the battery and nameplate, manufacturer and model of the device, and a brief description of the problem.
Our explanations summarize publications from professional associations, authorities, research institutions and cell manufacturers in a simplified manner.
- VDE Electrical Engineering Association: FAQ batteries. Link
- Federal Environment Agency: Lithium batteries and lithium-ion batteries (environmental tips for everyday life). Link
- Federal Environment Agency: Proper handling of lithium batteries and accumulators. Link
- Fraunhofer IIS: Battery management systems (product sheet). Link
- C. Kairies: Battery aging. Lecture, University of Paderborn, 2019. Link
- Panasonic: Specification of the lithium-ion cell NCR18650B (“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
- Cell manufacturer information: 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 factory ANR26650M1B; LiFePO4 cell IFR32700 (dealer information). Link
- UL (Underwriters Laboratories): Counterfeit Batteries eGuide. 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
- Lumafield: Battery Quality Report – CT analysis of 1,054 cells in 18650 format (2025). Link
- Manufacturer information: Shimano BT-E8035 and BT-E6010 (bike.shimano.com); Bosch PowerTube 500/750 (according to Canyon product pages); Makita BL1850B (according to RS Components). Link
Show us your battery.
A photo of the battery and the nameplate as well as a short description of the error are sufficient for an initial assessment.