3.7V 420mAh LiPo Battery (602040) - Rechargeable Lithium Polymer Cell with Protection PCB

Specifications

• Model Number: 602040P

• Chemistry: Lithium Polymer (LiPo)

• Nominal Voltage: 3.7V

• Fully Charged Voltage: 4.2V

• Rated Capacity: 420mAh (1.554Wh)

• Optimal Discharge Rate: 0.2C (approx. 84mA)

• Dimensions (L x W x H): 42mm x 20mm x 6mm

• Cable Length: ~50mm

• Connector: Open-ended (Bare wire)

• Built-in Protection: Overcharge, Over-discharge, Short Circuit

Key Applications and Projects

• Custom Macropads & Gamepads: Powering a Bluetooth-enabled ESP32 or Pro Micro inside a custom 3D-printed mechanical keyboard or media controller.

• Portable Environmental Monitors: Providing days of continuous power for a handheld device equipped with an OLED screen and a BME280 temperature/humidity sensor.

• Dashcams & Action Cameras: Acting as a high-quality replacement cell for commercial dash cameras or GPS trackers whose original internal batteries have degraded.

Unlock New Capabilities (Project Evolution)

• The Solar-Powered Weather Station: 420mAh is a fantastic amount of energy for a remote node! Evolve your outdoor project by pairing this battery with a TP4056 charging module and a waterproof 5V/1W solar panel. Because an optimised ESP8266 sending data once an hour only draws a tiny fraction of this battery's capacity, a single sunny day will easily recharge the cell, resulting in a weather station that can run indefinitely in your garden without ever needing to be plugged into the wall!

Package Includes:

• 1 x 602040P 420mAh 3.7V Lithium Polymer Battery pack (with internal protection PCB and 50mm open-ended wire)

FREQUENTLY ASKED QUESTIONS (FAQ)

1. What does "602040" mean? It signifies the standard dimensions of the bare internal cell: approximately 6.0mm thick, 20mm wide, and 40mm long. (The final length is roughly 42mm due to the folded protection board at the top).

2. What is the nominal voltage of this battery? The nominal (average operating) voltage is 3.7V.

3. What is the voltage when fully charged? A fully charged 1S LiPo battery will read exactly 4.2V on a multimeter.

4. Does this battery have built-in protection? Yes, there is a miniature protection PCB hidden under the yellow Kapton tape at the top of the battery.

5. What does the protection circuit actually do? It protects the battery chemistry from catching fire due to overcharging, prevents permanent damage from over-discharging, and cuts power instantly if a short circuit occurs on your output wires.

6. Are the wires open-ended or do they have a plug? This battery ships with 50mm open-ended (bare) wire leads. It does not come with a pre-crimped plastic JST connector.

7. Which wire is positive? The red wire is Positive (+), and the black wire is Negative (-).

8. What does "discharge at 0.2C" mean? "C" represents the total capacity of the battery. 0.2C means 20% of 420mAh, which is 84 milliamps (84mA). To get the absolute maximum lifespan and efficiency out of this battery, your circuit should optimally draw around 84mA continuously.

9. Will it break if my project draws more than 84mA? No. 84mA is the optimal rate for testing full capacity. The battery can easily handle higher bursts (like an ESP32 spiking to 250mA during a Wi-Fi transmission), but pulling very heavy currents constantly will drain it faster than the "420mAh" rating implies.

10. Can I charge this with a standard TP4056 module? Yes, but you should still ideally modify the TP4056. Standard modules push 1000mA (1A). While a 420mAh battery handles charge better than micro cells, charging at 1A (over 2C) will degrade it quickly. You should change the TP4056 programming resistor to output around 200mA to 400mA (0.5C to 1C).

11. Can I wire this directly to a 5V USB cable to charge it? ABSOLUTELY NOT. Applying raw 5V directly to a LiPo battery will cause it to swell, vent toxic gas, and catch fire. You must use a dedicated Lithium-Ion charger IC.

12. Can I power a 5V Arduino Uno with this? A standard Arduino Uno expects 5V. This battery only outputs 3.7V. You would need a "Boost Converter" module to step the 3.7V up to 5V.

13. What microcontrollers work best with this? Low-power 3.3V boards like the ESP32, ESP8266, Raspberry Pi Pico, and 3.3V Arduino Pro Minis are ideal companions.

14. How long are the wires? The flexible wire leads are approximately 50mm (about 2 inches) long.

15. Can I cut the wires to make them shorter? Yes. CRITICAL WARNING: Always cut the wires one at a time. Cutting both the red and black wires simultaneously with metal snips will short-circuit the battery!

16. Can I wire two of these in series to get 7.4V? It is highly discouraged to wire individual, internally protected LiPo cells in series. The two independent protection boards can conflict and cause charging and discharging failures.

17. Can I wire two in parallel to get 840mAh? Yes, but only if both batteries are measured with a multimeter and are at the exact same voltage (e.g., both exactly 3.8V) before connecting them. If they are different voltages, one will rapidly dump energy into the other, causing damage.

18. Is this battery waterproof? No. The silver foil pouch is sealed, but the top circuit board and the wire connections are fully exposed to the elements.

19. Why does my battery look puffy or swollen? LiPo batteries puff up when damaged, old, or severely over-discharged. If your battery swells like a balloon, stop using it immediately and safely recycle it.

20. How should I store this battery if I am not using it for a while? Never store LiPo batteries fully charged (4.2V) or fully dead (3.0V) for long periods. Store them at a "storage charge" of roughly 3.8V in a cool, dry, fire-safe location.