Battery knowledge
How a battery is structured, why cells age and how to store and charge your battery correctly: Here we explain the most important basics in an understandable way and with sources.
Understand what's in
your battery.
Clearly explained and supported by sources - summarized from publications from VDE, Federal Environment Agency, Fraunhofer, universities and cell manufacturers.
This is how a lithium-ion cell works
Each cell has two electrodes: the anode (mostly graphite) and the cathode (a metal oxide containing lithium). In between lies the separator, which prevents a short circuit; the electrolyte allows the lithium ions to pass through.[1]
- Loading: The ions migrate from the cathode to the anode and are deposited in the graphite.
- Unloading: They migrate back, and at the same time electrons flow across the external circuit - the device works.
Lithium-ion cells have no memory effect and low self-discharge.[1]
Series and Parallel: What “10S4P” Means
S (series) adds the voltage, P (Parallel) adds the capacity. The energy content results from voltage × capacity.[1]
Calculation: V = S × cell voltage, Ah = P × cell capacity, Wh = V × Ah; Cell count = S × P. Cell voltage and capacity must belong to the same chemistry and datasheet. The selection is an example calculation.[8] We check on a case-by-case basis whether a structure fits into your housing and your electronics.
Why we always replace all cells
Cells age differently – even identical cells under the same conditions. In a laboratory test with 48 identical cells, the variation in aging was similar over 25%.[5]
The BMS stops discharging as soon as the weakest group reaches its minimum voltage.[4] New and old cells mixed together therefore do not work well together. That's why we're completely re-equipping.
Simplified example: Group 6 has aged - the entire battery only supplies around two thirds.
Capacity and current carrying capacity
Capacity (Ah) describes how much charge a cell can store. The permissible continuous current (A) is a different quantity and depends on the cell type and the temperature conditions in the data sheet.
More Ah does not automatically mean more engine power. For a new assembly, the new cells must match the power requirements, the existing electronics and the charger. We use branded cells from LG and Sony.
The specific cell name and the interconnection are specified. Blanket electricity releases without a data sheet and temperature conditions are not promised here.
The battery management system (BMS)
Every lithium battery needs protective electronics. It keeps every cell within a safe range – and is often the reason why a battery “suddenly” switches off.
- voltage of each cell group
- temperature and current
- State of charge (SoC) and state of aging (SoH)
- Balancing the cell groups
- Switch off at limit values
Store and load correctly
Temperature when storing
Charging status during longer breaks
- For longer breaks 40–50 % Store charge and recharge to approximately 50% when necessary.[2]
- At 10-25°C Store in a dry place, not in direct sunlight and not in the refrigerator.[2]
- Do not drive empty - deep discharging shortens the service life.[2]
- Heat accelerates aging: For every 10 °C more, the speed of aging approximately doubles.[5]
Recognize warning signs
When used correctly, lithium batteries are safe. These signs mean: stop using, do not open.[3]
Cell formats in comparison.
The name of a round cell indicates its dimensions: 18650 means 18 mm in diameter and 65 mm in length.[1] Tap a format - all cells are drawn at the same scale.
There are also pouch and prismatic cells in many sizes.[1] We will clarify which cell is suitable and available for your battery on a case-by-case basis.
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.