Why This Bundle
The Molicel P42A is one of the strongest 21700 cells available — a 4200mAh typical capacity paired with a genuine 45A continuous discharge rating and a very low AC impedance (<15mΩ), making it a favorite for high-drain battery pack builds that need serious current without sacrificing runtime. Six of these cells need a charging setup that can keep up — at home and on the go. This bundle pairs 6 genuine Molicel INR21700-P42A batteries with the NITECORE UMS4 (a 4-bay smart LCD charger for fast, monitored charging at your desk) and the NITECORE UI1 (an ultra-compact single-slot charger for travel or topping off a spare cell). Together, all 6 batteries can be charged at once — 4 in the UMS4, and the 5th and 6th staggered through the UI1 — with full visibility into every cell's health.
Molicel INR21700-P42A Specifications
| Item |
Spec |
| Model |
Molicel INR21700-P42A (Flat Top) |
| Typical Capacity |
4200mAh |
| Minimum Capacity |
4000mAh |
| Nominal Voltage |
3.6V |
| Max Continuous Discharge |
45A |
| Standard Charge Current |
4.2A |
| Maximum Charge Current |
8.4A |
| Charge Cutoff Voltage |
4.20±0.05V |
| Discharge Cutoff Voltage |
2.5V |
| AC Impedance (1kHz) |
<15mΩ |
| Cycle Life |
~500 cycles at 4.2A charge/10A discharge to 80% capacity |
| Chemistry |
Li-ion, ultra-high-power |
| Cell Size |
21700 (approx. Φ21.2–21.7mm × 70–70.2mm, approx. weight 66.5g) |
| Terminal Type |
Flat Top only |
| Protection Circuit |
None (unprotected cell) |
| Typical Use |
Power tools, EVs/PHEVs, high-drain battery pack builds — Molicel specifies this as a pack-only cell for use with proper battery management |
Important: Molicel positions the P42A as a pack-only, high-power cell intended for use within a properly engineered battery management system (BMS) — not as a standalone consumer replacement cell for casual devices.
This is an unprotected cell — avoid mixing with batteries of a different brand, model, or charge state, and inspect the wrap for damage before every use to prevent short circuits.
The Chargers: NITECORE UMS4 + NITECORE UI1
NITECORE UMS4 — 4-Bay Smart LCD Charger
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USB-C input with QC support: up to 4,000mA total output, up to 3,000mA on a single bay with a QC adapter — the closest match here to the P42A's 4.2A standard charge current, though still below it
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Independent 4-bay control: charge and monitor each battery separately
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Real-time LCD display: shows battery health (Good/Poor), internal resistance, charging current, voltage, charged capacity, and charging time
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3 automatic charging modes: CC, CV, and -dV/dt, selected automatically based on battery type and charge level
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Manual adjustment: set charging voltage and current (300mA–3000mA) for specialized battery types
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Safety features: automatic internal resistance detection, reverse-polarity and short-circuit protection, overtime charging protection, and over-discharged battery activation/restoration
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Fire-retardant PC/ABS housing with built-in temperature regulation
NITECORE UI1 — Compact Single-Slot Charger
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Type-C input: automatically adapts to the optimal charging mode, works with power banks, solar panels, and USB adapters
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Up to 1000mA output with automatic CC/CV mode selection
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Trickle charging protects over-discharged cells and extends battery lifespan
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Over-discharge activation for protected Li-ion batteries
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Ultra-lightweight: just 40.5g — ideal for travel, a backup charge, or topping off the 6th cell while the UMS4 handles the other 4
Supported Battery Types & Voltage
NITECORE UMS4 — compatible with 3.6V/3.7V Li-ion, 3.8V Li-ion, 3.2V LiFePO4, and 1.2V Ni-MH/Ni-Cd batteries, including the Molicel P42A (21700) in this bundle: IMR/Li-ion/LiFePO4: 10440, 14500, 14650, 16500, 16340(RCR123), 16650, 17350, 17500, 17650, 17670, 17700, 18350, 18490, 18500, 18650, 18700, 20700, 21700, 22500, 22650, 25500, 26500, 26650, 26700 Ni-MH/Ni-Cd: AA, AAA, AAAA, C, D Output: up to 3,000mA per bay (QC mode) / 4,000mA total
NITECORE UI1 — compatible with 3.6V/3.7V Li-ion/IMR batteries, including the Molicel P42A (21700): 10340, 10350, 10440, 10500, 12340, 12500, 12650, 13450, 13500, 13650, 14430, 14500, 14650, 16500, 16340(RCR123), 16650, 17350, 17500, 17650, 17670, 18350, 18490, 18500, 18650, 20700, 21700, 22500, 22650, 25500, 26500, 26650 Output voltage: 4.2V±1% · Output current: up to 1000mA
Compatibility Notes
The UMS4's bays and spring-loaded contacts are sized to accommodate 21700 cells like the P42A without any adapter, and the UI1's slot fits the same length range. Given this is a high-power cell with a demanding 4.2A rated charge current, neither charger will match the P42A's full rated charge speed, but the UMS4 (up to 3,000mA on a single occupied bay) gets meaningfully closer than the UI1 (up to 1,000mA). We'd suggest running your most time-sensitive cells through the UMS4 and treating the UI1 as a slower backup for the batteries you're least in a hurry about.
What's Included
- Molicel INR21700-P42A Battery × 6
- NITECORE UMS4 4-Bay Charger × 1
- NITECORE UI1 Single-Slot Charger × 1
- USB-C Charging Cables × 2
- User Manuals × 2
Safety Tips
- Store batteries in a proper case, keeping them away from loose metal objects to prevent short circuits
- Never disassemble, puncture, burn, or submerge the batteries
- Charge only with genuine, compatible chargers such as the NITECORE UMS4 and UI1
- The P42A is an unprotected, ultra-high-power cell intended for use within a properly engineered battery pack with its own BMS — do not use it as a standalone replacement cell in casual consumer devices
- Never discharge below 2.5V or charge above 4.2V
FAQ
Q: Can I charge all 6 batteries at the same time? A: Yes. The UMS4 charges 4 batteries independently and simultaneously, while the UI1 can charge a 5th battery alongside it — or you can stagger the 5th and 6th through the UI1 if only one is used at a time.
Q: Is the P42A meant for use in standalone devices like flashlights? A: Molicel positions the P42A as a pack-only cell intended for use within a properly designed battery management system, not as a standalone drop-in cell for casual consumer devices. It's built for power tools, EVs/PHEVs, and engineered high-drain battery packs.
Q: Are Molicel P42A batteries safe to charge in both chargers? A: Yes. Both the UMS4 and UI1 automatically recognize Li-ion chemistry and apply the correct charging voltage (4.2V) and current for P42A cells — though neither will reach the cell's full 4.2A rated charge speed.
Q: Will 21700 batteries fit in both chargers? A: Yes. Both the UMS4 and UI1 are sized to accommodate 21700 cells like the P42A without any adapter.
Q: What's the difference between the UMS4 and UI1 in this bundle? A: The UMS4 is a 4-bay charger with an LCD screen showing detailed real-time data (battery health, internal resistance, voltage, capacity) and faster QC charging up to 3,000mA on a single bay. The UI1 is a single-slot, ultra-compact charger (40.5g) best suited for travel or a slower backup charge.
Q: How do I check if a battery is degraded? A: The UMS4's LCD display shows battery health as "Good" or "Poor" along with internal resistance readings, making it easy to spot cells that have aged or lost performance.
Q: What's in the box? A: 6 Molicel INR21700-P42A batteries, 1 NITECORE UMS4 charger, 1 NITECORE UI1 charger, 2 USB-C charging cables, and user manuals for both chargers.
