USB-C Rechargeable Battery Quickpost

Dec 6, 2025
2 min read

Key Findings

USB-C rechargeable batteries have built-in battery charger and voltage converter electronics
They deliver a constant 1.5V output, unlike NiMH batteries that have a varying voltage
Measured capacities are significantly lower than advertised, with round-trip efficiencies around 63-72%
They have some advantages like a flat discharge curve and no leakage, but also disadvantages like abrupt voltage drop and electrical noise
These batteries cannot negotiate power with a USB charger, requiring a USB-A to USB-C cable rather than USB-C to USB-C

Background

The author discovered USB-C rechargeable batteries and decided to conduct various tests and measurements to characterize their performance. These batteries have a USB-C connector for recharging, unlike traditional NiMH batteries that require a separate charger.

Voltage Characteristics

The USB-C rechargeable batteries deliver a constant 1.5V output during discharge, unlike NiMH batteries that have a varying voltage. The author observed a distinct pattern in the voltage ripple, suggesting the presence of a switching-mode power supply circuit within the batteries.

Capacity Discrepancy

Discharge tests revealed that the measured capacities of the AA and AAA batteries were significantly lower than the advertised values. The AA batteries delivered around 1500 mWh, compared to the advertised 3400 mWh, while the AAA batteries delivered 478 mWh against the 1200 mWh claim.

Round-Trip Efficiency

The author calculated the round-trip efficiency (RTE) of the batteries, which ranged from 63% for the AAA batteries to 72% for the AA batteries. This indicates substantial energy losses during the charging and discharging processes.

Advantages and Disadvantages

The USB-C rechargeable batteries have some advantages, such as a flat discharge curve, no battery leakage, and the ability to charge without a separate charger. However, they also have disadvantages, including the abrupt voltage drop when fully discharged, the inability to negotiate power with a USB charger, and the presence of electrical noise.

Sources

https://blog.didierstevens.com/2025/12/06/quickpost-usb-c-rechargeable-batteries/
https://blog.didierstevens.com/2025/12/05/quickpost-usb-electric-razor/