A high-drain 18650 has to do more than post a big amp figure on a listing. In a torch, power tool pack or custom battery build, it needs to hold voltage under load, manage heat sensibly and remain consistent from cell to cell. This P28A cell review looks at why the Molicel INR18650-P28A remains a strong all-round choice when current demand matters more than chasing maximum runtime.
The P28A is a 2800mAh 18650 lithium-ion cell with a continuous discharge rating commonly specified at up to 35A. That places it firmly in the high-drain category. It is not the highest-capacity 18650 available, but it offers a useful balance of capacity, output and thermal performance for builds that would push a typical 3000mAh-plus cell too hard.
P28A cell review: key specifications
The P28A uses INR chemistry, has a nominal voltage of 3.6V and charges to 4.2V. It is generally supplied as an unprotected flat-top cell, so it is intended for equipment with appropriate low-voltage protection or for battery packs built with a correctly selected BMS.
Its 2800mAh rated capacity sits below capacity-first 18650 cells, but that is the trade-off for its high current capability. At moderate loads, the difference in runtime versus a 3000mAh or 3500mAh cell may be noticeable. At high loads, however, a capacity-focused cell can suffer greater voltage sag, run hotter and deliver less usable energy than its label suggests.
For most makers, the figure worth understanding is not simply the 35A rating. It is how the cell behaves at the current your device actually draws. A 5A torch, a 15A cordless tool and a 25A single-cell vape device place very different demands on an 18650.
Where the P28A performs well
The P28A has earned its reputation because it remains comparatively stable when demand rises. Under hard discharge, voltage drop is lower than many general-purpose 18650 cells. This helps devices maintain output and reduces the chance of a BMS or device low-voltage cut-off activating earlier than expected.
That makes it a sensible candidate for high-output torches, power-tool battery rebuilds where the original design permits it, portable power projects, RC applications and properly engineered e-bike or scooter packs. In multi-cell packs, lower sag also helps the pack deliver useful power without placing all the stress on a small number of parallel cells.
Heat is the other practical advantage. Every lithium-ion cell warms under load, and a 35A discharge is demanding even for a cell designed to handle it. The P28A is better suited to those loads than a high-capacity alternative, but it is not immune to poor pack design. Tight cell spacing, undersized nickel, weak welds, inadequate airflow and a BMS below the required current rating can all create heat problems before the cells themselves become the limiting factor.
A claimed continuous rating should never be treated as a target for every build. For long periods of operation, designing with current headroom is wiser than running cells continuously at their maximum published limit. A pack that needs 35A continuously from one cell in hot Australian conditions deserves a closer look at cooling, duty cycle and whether a larger cell format, such as a 21700, would be the better solution.
Capacity and runtime: the real compromise
At 2800mAh, the P28A offers respectable capacity for a high-drain 18650. It is a practical middle ground, rather than a specialist runtime cell. If your device draws modest current and must run for as long as possible between charges, a higher-capacity 18650 will often be a better buy.
The difference is especially clear in low-drain equipment such as basic LED lights, storage projects, sensors or low-power electronics. These applications do not need 35A capability, so paying for it provides little benefit. A quality 3200mAh to 3500mAh cell may give longer service between charges.
The calculation changes when load rises. Capacity ratings are measured under controlled discharge conditions, usually at relatively low current. A cell with a larger stated mAh figure can lose ground under a demanding load because more energy is wasted as heat and voltage drops faster. In a high-drain device, the P28A's usable runtime can be closer to, or better than, a nominally larger cell that is being pushed beyond its comfort zone.
Cell format and compatibility checks
The P28A is an 18mm-class, 65mm-long 18650 cell, but do not assume every 18650 device will accept it. As a flat-top unprotected cell, it is shorter than a protected button-top version. Some torches and battery holders need the raised positive terminal of a button-top cell to make reliable contact. Other devices are designed specifically for flat-top cells.
Check the original cell configuration before ordering. Measure the old cell where possible, inspect the positive contact and confirm whether the device expects protection electronics. A protected 18650 may be physically too long for equipment designed around an unprotected cell, while an unprotected P28A may be unsuitable for a device that relies on the cell's own protection board.
For pack building, use matched P28A cells from the same model and batch where possible. Do not mix old and new cells, different brands or cells with substantially different capacities in the same series or parallel group. Matching matters because the weakest cell in a pack can be overworked during charging and discharge.
Charging and pack-building considerations
Charge the P28A only with a lithium-ion charger set up for standard 4.2V charging. Use a charger with independent channels when charging loose cells, particularly if cells have different states of charge. Avoid cheap USB leads or improvised charging arrangements that provide no reliable charge termination.
For a multi-cell battery pack, the charger, BMS, wiring, nickel strip and connectors must all suit the pack's series count and expected current. A 35A-rated cell does not make a 35A pack if the BMS is rated below that figure or the nickel strip becomes the bottleneck. Spot welding is the preferred method for joining cylindrical cells. Soldering directly to a cell can transfer damaging heat into the can and internal structure unless performed with appropriate equipment and technique.
Mechanical protection matters as much as electrical specification. Use fish-paper insulation, positive terminal rings and suitable cell spacers where required. Replace damaged wraps before a cell is used. The metal can is the negative terminal, so a tear in the wrap near the positive end can create a short circuit against a nickel strip or metal holder.
Never charge unattended, do not use cells that are dented, swollen, leaking or unusually hot, and store loose 18650s in proper plastic cases. Keeping cells out of a pocket, tool bag or ute console with loose metal items is basic but worthwhile risk control.
Is the P28A the right choice?
Choose the P28A when your project needs a genuine high-drain 18650 with enough capacity for practical runtime. It suits users who value voltage stability and current capability over the biggest possible mAh number. It is particularly compelling where a device draws repeated high-current bursts or sustained moderate-to-high current.
Choose a higher-capacity cell if the load is low and runtime is the priority. Choose a 21700 if the enclosure allows it and your build needs substantially more capacity or current headroom. A larger format can reduce the stress placed on each cell, simplify pack design and improve thermal margins.
For Australian repairers and makers, buying correctly specified cells from a specialist supplier is preferable to relying on reclaimed packs or vague no-name listings. TinkerTech AU can help keep the selection process straightforward by pairing cell format, capacity and discharge rating with the parts needed to build safely.
The P28A is not a magic answer to every 18650 application. It is a capable high-drain cell that rewards sensible design. Match it to the load, allow headroom in the pack, and treat every insulation, charging and connection detail as part of the battery system rather than an afterthought.