Phone Charger Current Comparison

I bought a spare phone charger on eBay several months ago, and I always wondered if that charger was a genuine product or a counterfeit. Looking at it there’s no way of telling. The eBay purchased charger has all the labels just like the original.

I then figured that a way to confirm the charger is genuine is to verify it can charge at the same current level as the charger that came in the box with the phone. And that’s what I set out to do in this experiment!

I’ll do a side-by-side comparison of the charging current of each charger, and I’ll plot the results for easy comparison. In order to do that I’ll use an Arduino Uno board to collect the current and will plot the acquired data in an Excel spreadsheet so that it is very easy to see how each charger compare against the other!


Experiment Description

In my experiment I’ll charge up an HTC Thunderbolt I have laying around.  Both the original charger shipped with the phone as well the replacement are HTC Charger Model # TC U250. Here’s what it looks like:

HTC Charger Model TC U250

In this document the original charger is referenced as carger #1 and the eBay replacement is referenced as charger #2.

Charger #2 was bought on eBay from a seller called topcooltech. That seller seem to no longer be selling on eBay. I paid $3.58 for the charger, and that is with free shipping from China.

snapshot of my eBay purchase

Side-by-side photo

Just as a reference blow is the label of both the Charger 1 (the original) and Charger 2 (the replacement).

The labels are a bit different, but the replacement does not look like an obvious counterfeit. 


Test Method

In order to read the current flowing between the charger and the phone, I’ll use an Arduino board with an USBar. USBar is a current sense shunt adapter that connects between USB devices and output a 0-5v signal corresponding to the current it senses so that Arduino can read it.

Arduino takes the analog value and sends serial (USB cable) to the PC. In the PC I’m running the PLX-DAQ, which is one of my favorite Arduino tools.

Photo of actual setup 

USB current shunt

Test Setup for Charger comparison

Test Conditions:

  • Phone was powered off.
  • Phone battery completely discharged.



Drum rolls…..

The graph shows that charger 1 delivering a solid 275mA of charging current. Charger 2 does seem to have enough current, however it fluctuates from 250mA to 375mA.

These chargers definitely produce a different charging characteristic. My educated guess is that charger 2 behavior could have a negative effect to phone or battery.


  • Transient at 7sec seem so happen every time I plug in the phone to start charging. It may be normal behavior of phone or charger’s algorithm.
  • Charger #1, the original charger, only delivered 275mA vs the 1000mA stated in the label. I have no idea why that is.

Bonus Test: Battery Pack Charging Current

I had a battery pack (bought at Microcenter) laying around, so I decided to plug that in and see how it’s charging current compares to the phone charger.

The pack manufacturer is unclear. I’d guess it is a company called “Power”. Further, the label reads output current is 800mA

Here’s the phone setup looks like:

Phone Charging using Battery Pack


Wow! The battery pack delivered 700mA vs only 275mA the original charger did! How to explain that?


Downloads: (coming soon)

  • Arduino Sketch to measure current and plot into Excel:
  • Excel Spreadsheet with Serial in