RC Battery Parallel Pack Calculator
Calculate combined mAh, C-rating, and max discharge current for RC LiPo batteries in parallel.
Returns safe current limits and runtime gain over a single pack.
How RC Battery Parallel Packs Work
Connecting LiPo batteries in parallel increases total capacity and maximum discharge current while keeping the voltage the same. This is commonly done in large RC planes, boats, and heavy-lift drones that need more energy than a single pack provides.
Parallel Connection Rules
Voltage stays the same:
V_total = V_single (all packs must be the same cell count / voltage)
Capacity adds up:
Capacity_total_mAh = Capacity_per_pack × Number_of_packs
Maximum continuous discharge adds up:
Max_Amps_total = Max_Amps_per_pack × Number_of_packs
Where Max_Amps_per_pack = (Capacity_mAh / 1000) × C_Rating
C-Rating Explained
The C-rating indicates how fast a battery can safely discharge relative to its capacity:
- A 2200 mAh battery with a 25C rating can deliver: (2200/1000) × 25 = 55 amps continuous
- Two of these in parallel: 110 amps continuous, 4400 mAh total
Worked Example
Three 5000 mAh 4S (14.8V) 30C packs in parallel:
- Voltage: 14.8V (unchanged)
- Total capacity: 5,000 × 3 = 15,000 mAh (15 Ah)
- Max discharge per pack: (5000/1000) × 30 = 150A
- Total max discharge: 150 × 3 = 450A
- Total energy: 14.8V × 15Ah = 222 Wh
Important Safety Rules
| Rule | Why |
|---|---|
| Same cell count (S) | Different voltages cause dangerous current flow |
| Same or similar capacity | Unmatched packs cause uneven load |
| Match voltage before connecting | Even 0.1V difference causes a large inrush current |
| Same C-rating preferred | Weaker pack gets stressed during high-draw maneuvers |
Charging a Parallel Pack
The charge time is the easy part and it is the same as for any single pack, because a C rate is defined relative to capacity. At 1C the current scales with the pack, so the clock does not move: about 1.1 hours, where the extra 10% is the CV (constant voltage) phase at the end, when current tapers off and the last of the charge goes in slowly. The LiPo charge time calculator uses the same 1.1 factor.
The part that catches people out is the current, not the time.
Charge current at 1C (A) = Total capacity (mAh) ÷ 1000
Three 5,000 mAh packs in parallel are a 15,000 mAh pack, and charging that at 1C needs a 15 A charger. Plenty of popular hobby chargers top out at 10 A, and a lot of the cheaper ones at 5 A or 6 A. Your charger’s wattage matters too: 15 A into a 4S pack at 16.8 V is roughly 250 W, which is beyond many single-port units.
If your charger cannot supply it, nothing breaks. You simply charge below 1C and it takes proportionally longer, which is gentler on the cells anyway. A 15,000 mAh pack on a 5 A charger is charging at 0.33C and will take a bit over three hours.
Charge a parallel pack through a proper parallel charging board with the balance leads connected, and only ever join packs that are already at matched voltage.
Weight Consideration
Total pack weight = Single_Pack_Weight × Number_of_Packs. In RC aircraft, every gram matters for flight time and handling. Parallel packs are most common in boats and ground vehicles where weight is less critical.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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