How Samsung ruins the Galaxy Watch 4’s best charging trick

For all the slick Wear OS tricks and comprehensive fitness features that the Samsung Galaxy Watch 4 Classic offers, battery life is somewhat of a letdown. Even with an average day of usage involving continuous heart rate monitoring and GPS tracking for outdoor workouts, you will find yourself looking for the charging puck at the end of the day.

Samsung ships a wireless charging puck in the retail package. But this one takes about two hours to fully juice up the 46mm variant of the Galaxy Watch 4 Classic. That’s a bit too slow, considering the fact that smartwatches half its asking price — such as the divisive OnePlus Watch — take just about an hour to go from empty to 100%.

samsung reverse wireless power sharing

My point here is that you might want to buy an extra charger for your office desk, just to make sure it doesn’t run out of juice midway through a busy day. Thankfully, the Galaxy Watch 4 and Watch 4 Classic can be juiced up by a phone without any wire hassles. Just put it at the back of your phone, and watch the smartwatch trickle charge. But as convenient as that sounds, there are a lot of caveats.

The losses and gains

Let’s start with the charging speed first. Samsung offers a feature called Reverse Power Sharing on its phones that support wireless charging. Just enable it from the quick settings panel, put your smartwatch or earbuds case on the phone’s rear panel, and watch the energy transfer happen in real-time.

But the rate of power transfer is quite slow. I performed three test runs of the Galaxy Watch 4 Classic (46mm) being brought to life from 0% power to full charge, and it took the Galaxy S22 Ultra nearly three and half hours to do the job, on average.

Here’s the most recent breakdown of the charging process, conducted in a room at 75 degrees Fahrenheit, and both the devices lying still.

Time on the clockBattery level on  Galaxy Watch 4 ClassicBattery level on Galaxy S22 UltraTemp. of phone (in Fahrenheit)
10:30 am0%100%96.8 degrees
10:50 am7%95%102.2 degrees
11:30 am20%88%102.2 degrees
11:42 am25%86%104 degrees
12:28 pm50%76%104 degrees
12:51 pm67%71%104 degrees
01:15 pm80%63%105.8 degrees
02:10 pm100%56%105.8 degrees

From the table, it might appear that charging the Galaxy Watch 4 Classic’s tiny battery sucks up nearly all the power from Galaxy S22 Ultra’s 5,000 mAh battery. But a healthy portion of that battery drain is due to tasks running in the background and idle battery consumption. Expect that number to be much higher for a phone with a smaller unit such as the Galaxy S22.

During the charging process, the temperature of the phone’s back initially rose by around 4 degrees but stabilized after that point. But there are outlier scenarios. While working in a garden with the outdoor temperature at a searing 93 degrees Fahrenheit, the rear panel’s temperature rose by about 9 degrees, all the way up to 113 degrees Fahrenheit.

However, that rise in temperature is temporary and stays that way as long as the phone’s wireless charging coil is transferring power. Within 5 to 10 minutes, things return to normal. In a nutshell, heating was not an issue during the test phase.

A convenience burdened with caveats

The key takeaway here is that reverse power sharing is nothing short of a lifesaver for a Galaxy smartwatch running low on juice. If you have the patience to keep your phone and smartwatch untouched for an hour, you will get at around 20% to 25% power transferred to a compatible Samsung smartwatch.