#1 · Why Does a 24V Battery Say 25.6V?
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- "24V" and "48V" are names for the machine's voltage system. The 25.2V, 25.6V, 50.4V and 51.2V on a spec sheet are the battery pack's nominal voltage — one cell's voltage multiplied by the number of cells in series — so two "24V-class" packs can carry different numbers depending on the cell type.
- Whether a pack fits the machine is decided by its operating voltage range, not its nominal voltage. A pack's voltage is highest right after a full charge and lowest at the end of discharge, and that whole range must sit inside the allowed input range of the motor driver (or controller).
- POWERCRAFT's standard lineup carries both 25.2V (Li-ion 7S) and 25.6V (LiFePO₄ 8S) in the 24V class, and both 50.4V (Li-ion 14S) and 51.2V (LiFePO₄ 16S) in the 48V class. Compare the voltage ranges in the table below; if your machine needs 21.6V (Li-ion 6S) or 46.8V (Li-ion 13S), please contact POWERCRAFT for a custom build.
1. When the spec sheet does not say "24V"
Robot and AGV power systems usually run on a "24V" or "48V" system voltage. The motor driver, controller and sensors are all specified by that name, so it is natural to look for a "24V battery". Then the spec sheet says 25.2V or 25.6V, and the question comes up: is this really 24V?
They are the same thing described at two different levels. 24V is the name of the machine's voltage system; 25.2V and 25.6V are the nominal voltages of the batteries that go into it. That is also why the "System voltage" filter in the POWERCRAFT shop reads 12V, 24V and 48V. Choose by system voltage in the filter, and check the pack's nominal voltage on the spec sheet.
2. Nominal voltage = cell voltage × cells in series
The nominal voltage of a lithium battery pack is one cell's nominal voltage multiplied by the number of cells connected in series (S). A LiFePO₄ cell is rated 3.2V nominal (2.8–3.65V) and a Li-ion cell 3.6V nominal (3.0–4.2V). So in the same "24V class", a Li-ion pack uses 7 cells in series (7S) for 25.2V, while a LiFePO₄ pack uses 8 in series (8S) for 25.6V.
| System voltage | Cell type | Series | Nominal voltage (spec sheet) | Operating range |
|---|---|---|---|---|
| 12V | LiFePO₄ | 4S | 12.8V | 11.2–14.6V |
| 24V | Li-ion | 7S | 25.2V | 21.0–29.4V |
| 24V | LiFePO₄ | 8S | 25.6V | 22.4–29.2V |
| 48V | Li-ion | 14S | 50.4V | 42.0–58.8V |
| 48V | LiFePO₄ | 16S | 51.2V | 44.8–58.4V |
3. What you actually check is the operating range
Nominal voltage is closer to a label. A battery sits above its nominal voltage right after a full charge and falls as it discharges until it reaches the cut-off voltage.
The datasheet of the motor driver (or controller) states an allowed input voltage range. There is one thing to check: is the battery's operating voltage range compatible with the driver's operating voltage range? If it is not, the motor drive may stop right after a full charge or before the pack reaches its cut-off voltage.
Chargers are matched to the charging voltage, not the nominal voltage. The "standard charging condition" line of the spec sheet is that value — for example, 29.2V for a 25.6V pack and 58.4V for a 51.2V pack. If the charger's output voltage differs from this, the pack will not reach full charge, or overcharging may lead to a safety incident.
4. What is the difference between 25.2V and 25.6V?
Both are built for 24V systems. The difference comes from the cell type, and as the table shows, the operating ranges differ slightly: Li-ion 7S is 21.0–29.4V, LiFePO₄ 8S is 22.4–29.2V. If the driver's allowed input range covers both, either pack can be used, and the next choice moves on to the characteristics of each cell type — size and weight per capacity, cycle life, operating temperature and so on — which the next article covers.
5. Custom builds follow the same voltage system
Custom build projects carry the nominal voltage in their titles too. A 25.2V 100Ah pack with a built-in DC-DC charging module and CAN communication for an autonomous mobile robot is a 24V system (Li-ion 7S), and a 50.4V 30Ah pack with a 24V DC-DC module for an AGV runs the main drive on a 48V system (Li-ion 14S) with auxiliary devices on 24V. Standard or custom, the reading order is the same: machine system voltage → nominal voltage → operating range.
24V and 48V are the names of machine voltage systems; 25.2V, 25.6V, 50.4V and 51.2V are battery nominal voltages — cell voltage times cells in series. Confirm fit by checking that the spec-sheet operating range sits inside the driver's allowed input range, and check the charging voltage specification for the charger.
— all 49 standard packs can be filtered by voltage, capacity and cell type. If you need a voltage, size or communication option that is not in the standard lineup, browse the POWERCRAFT custom build projects and leave a specification request.