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Knowledgebase

Stub Battery terms 101 | Batteries 03/11/25 6mo ago  E-HP
Preface: If the deal is too good to be true, it is. A general rule, currently, for a pack made with name brand 18650 cells (Samsung/Sanyo/Panasonic/LG/Sony) $5 x the total number of cells in the pack is the minimum you should expect to pay. If the pack is made with generic Chinese "highest quality A grade cells", or similar description, you might expect to pay $3 x the total number.​

Terminology: Most lithium ion packs use series of cells that make up the pack voltage; typically 36V, 48V, 52V, and 72V (multiples of 12V). Respectively, the number of corresponding series cells for those voltages are 10, 13, 14, and 20. The total pack capacity (amount of energy stored) is based on how many series groups are placed in parallel, and the capacity of each cell. Packs may be described by voltage and capacity (52V 15Ah) or by their component make up (for example 14S5P), which describes the number of series cells (14S) and the number of parallel group (5P). In the example below, lithium ion cells are used.​

"S", combined with the voltage specs for the cells used, will determine the voltage of the pack. So, 14S means 14 series cells, and in this example, each with a nominal voltage of 3.7V; 14 x 3.7 = 51.8, or a 52 volt pack.​
"P" is used to determine the current stored (Ah), and discharge capability of the pack (A). This again depends specs of the cells used (for example 3000mAh, with a discharge capability of 10A). So for a 5P pack, 3000mAh times the number of parallel groups (5 in this example); yields 5 x 3000 = 15000mAh or 15Ah stored. 5 x 10 = 50A discharge capability.​
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So the example pack, using lithium ion cells, each with 3500mAh stored and 10A discharge capability, in a 14S5P configuration provides 15Ah with a 50A max output.​
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BMS (Battery Management System)​
Manages a battery pack, monitoring voltages and currents, at both pack and cell levels, in order to protect the cells, keeping them within their specified ranges. The BMS may also perform balancing functions in order to keep all cells in the pack at the same voltage.​
Common Port (single) vs Separate Port (dual) BMS​
A common port BMS has a charge port and discharge port electrically connected. If the BMS detects high voltage, it cuts off charging, if it detects low voltage, it cuts off load. The separate port BMS has the load and charge port electrically separate. The BMS It can shut off charging at a specified voltage. I can disconnect load due to low voltage, but not disconnect charging. Common vs Separate port become more relevant when battery packs are combined either in series or in parallel, and how protection of the packs can be maintained. In most situations where packs are combined, common port BMSs can continue to protect the packs independently. Some two pack configurations can still work with one pack having a common port, while the second uses a separate port BMS.​

Notes on battery safety:
  • Don't leave your bike charging while unattended. If you're leaving the house while charging, just set it on fire yourself when you leave, so you won't be surprised when you get home.
  • Don't ignore/dismiss/condone odd battery behavior. Don't make assumptions about the cause. It almost always will lead to issues if not addressed.
  • Don't assume charging will correct issues, other than balancing. Don't charge until the problem is properly diagnosed and corrected.
  • A battery shouldn't be getting hot while discharging, unless you are discharging near or above the rated output. The battery should be taken out of service until diagnosed. It could lead to a fire while riding.
Cell database: Cell Database