How to make 3.2v lithium ion cells to 12v battery packs?
lithium ion cells are the basic building blocks for lithium ion battery packs. In this blog, we will take prismatic 3.2v lithium cells making 12v battery packs for example to explore how is the professional manufacturer to produce the lithium ion battery packs.
Two connections of lithium ion cells
1.cells in series
When assembly the lithium ion cells to series connections, lithium ion battery packs won’t change the amp-hour rating, but will raise the voltage of the battery system. Please always keep in mind that with series connections, each battery needs to have the same voltage and capacity rating, or you can end up damaging the battery. In this kind of connection, the positive terminal of a 3.2v lithium cells is connected to the negative terminal of the next cell until the desired voltage is achieved. For instance, if we want a battery packs 12v, we need to use 4pcs 3.2v 100ah lifepo4 rechargeable battery cells with series connection.
2. lithium ion cells in parallel
When connecting 3.2v lithium cells in parallel, the positive terminals are connected together, and the negative terminals are connected together until the required capacity is reached. Parallel connection means connecting 2 or more 3.2v lifepo4 battery cells together to increase the ampere hour capacity of the battery pack, but the voltage remains the same. Therefore, two 3.2v 100ah battery cells in parallel connection would create a 3.2v lifepo4 battery 200ah pack.
Professional laser welding
Laser welding is a good choice for joining battery tabs during prismatic lithium ion cells to battery pack assembly. The process is fast and efficient. It produces high-strength welds for all material combinations. The process is easily adapted to a broad range of joint designs. Ordinary welding techniques can cause heat damaging the anode/cathode. But with laser welding, there is no heat damaging the anode/cathode. It is the most advance technology for welding 3.2v lifepo4 rechargeable battery cells. So, for this reason, most professional manufacturer are use laser welding to assembly the 3.2v lithium cells. As to our OSM company, we also use this technology to make 3.2v lifepo4 cells to 12v or 48v battery packs.
The battery packs controller, BMS
When a lithium-ion cell is fully charged, its voltage begins to rise further, which may lead to electrode damage. If the charge of the entire battery is stopped when only one cell is fully charged, the remaining cells do not reach full charge and the battery will operate below peak capacity. A well-designed BMS will ensure each cell safely and fully charges before the entire charging process is complete.
BMS just like the brain of 12 volt lithium ion battery packs which monitors and manages all the battery’s performance. It manages real-time control of each battery, communicates with external devices, manages SOC calculations, measures temperature and voltage, and so on. The selection of BMS determines the quality and life of the final rechargeable battery packs.
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How many 3.2V cells make 12V, 24V and 48V?
A LiFePO4 cell is 3.2 V nominal, so the string length follows directly from the target voltage. Four cells give a nominal 12.8 V, which is what the industry calls a “12 V” LiFePO4 pack:
| Nominal pack voltage | Series cells (3.2 V) | Actual nominal | Charge voltage (3.65 V/cell) |
|---|---|---|---|
| 12 V | 4S | 12.8 V | 14.6 V |
| 24 V | 8S | 25.6 V | 29.2 V |
| 48 V | 16S | 51.2 V | 58.4 V |
| 72 V | 22–23S | 70.4–73.6 V | 80.3–83.95 V |
3.2V to 12V: the series connection maths
In a series string the voltages add and the amp-hours stay the same. Four 3.2 V 100 Ah cells in series therefore make a 12.8 V 100 Ah pack — the same 100 Ah, but four times the voltage and four times the energy (1.28 kWh instead of 0.32 kWh). The rule to remember: series raises voltage, not capacity.
One condition is non-negotiable — every cell in the string must share the same chemistry, capacity and state of charge. Mismatched cells cause the weakest one to be driven to the voltage extremes, which is the usual root cause of a pack that fails prematurely.
Adding capacity in parallel
Parallel connection is the mirror image: amp-hours add and the voltage stays the same. Two 12.8 V 100 Ah packs in parallel give 12.8 V 200 Ah. For larger builds the manufacturer first strings cells in series to reach the voltage, then parallels those strings to reach the capacity — written as, for example, 4S2P for a 12 V 200 Ah pack. The larger prismatic format used for packs like our 51.2 V 150 Ah deep-cycle battery is the same principle scaled up.
BMS wiring for a 4S 12V LiFePO4 pack
- Sense leads — one wire per cell junction, so a 4S pack needs five sense connections (B−, B1, B2, B3, B4).
- Charge and discharge paths — either a common port or separate ports, depending on the BMS design.
- Voltage windows — the BMS must be programmed for LiFePO4 (2.5 V cell cutoff, 3.65 V charge limit), not for lead-acid voltages.
- Balancing — a balancing current of 30–100 mA is usual for small 4S packs; larger currents for big prismatic strings.
Choosing the right BMS is the part that decides whether the finished pack lasts; the criteria are set out in BMS for a lithium battery pack.
A 12V LiFePO4 pack compared with a 12V lead-acid battery
| Property | 12 V LiFePO4 | 12 V lead-acid |
|---|---|---|
| Usable depth of discharge | 80–100 % | About 50 % |
| Cycle life | 2,000–6,000 | 300–500 |
| Weight | About one third | Baseline |
| Maintenance | None | Watering, equalising |
| Charge voltage | 14.6 V (4S) | 13.8–14.4 V |
The voltage numbers are close enough that a lead-acid charger will “work” on a 4S LiFePO4 pack — and that is exactly the trap, because a lead-acid profile includes equalisation and float stages that are wrong for lithium. The charger must be set for LiFePO4. A worked example of the same 4S logic in a high-current application is our 12 V 20 Ah automotive LiFePO4 battery.
3.2V to 12V pack FAQs
Can I connect 3.2V cells directly to get 12V?
Yes, four in series produce a nominal 12.8 V pack. The cells must be matched in chemistry, capacity and state of charge, and the pack must have a proper 4S BMS.
How many 3.2V 100Ah cells do I need for a 12V 100Ah battery?
Four, connected in series. Series raises the voltage without changing the amp-hours, so the finished pack is 12.8 V 100 Ah.
Do I need a BMS for a 4S pack?
Always. Without cell-level over-charge, over-discharge and balancing protection a single cell can be driven into permanent damage or a safety failure.
Need a quote? Tell us the pack voltage, capacity and application and we will build the right LiFePO4 configuration — factory-direct, no obligation.
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