The Galaxy S21 battery life tests bring unwelcome surprise

Consequently, Qualcomm boasts up to three times performance per watt improvement when compared to the Snapdragon 865 in the S20 and ditto for Samsung's other S21 chipset, the Exynos 2100. Add to these the lower resolution that the Galaxy S21 uses, and the adaptive refresh rate screen technology, and it's party time.The battery unit of the S21, whose model number is EB-BG991ABY, sound familiar? It is actually the 4000mAh EB-BG980ABY piece that is found inside the S20 as well, so battery life should be about the same, right? We thought not, for the reasons below, but the actual testing proved that the S21 battery life isn't better than what the S20 offers, and is actually worse in some cases. 

Galaxy S21 vs Galaxy S20 battery life efficiency

The FHD (S21) vs QHD (S20) display

While the Galaxy S20 is equipped with an overkill 1440p resolution on a comparatively tall and narrow 6.2" screen, Samsung went the smarter route this time around, and is launching the S21 with a 1080p panel. The lower pixel density makes for a much more frugal panel, as there are 1MM+ less pixels to light up and manage with the graphics subsystem. Our own battery tests show that phones with FHD screens perform 20-30% better in terms of battery life than those with QHD or higher screen resolutions when we average out for the battery capacity difference.

Tap the lower band of that range, and the S21 should outlast the S20 with two hours, hitting a tenner in our browsing and scrolling battery test, all other things being equal. The point is they won't be equal, however.

The 5nm (S21) vs 7nm (S20) processor

Compared to the second-gen 7nm (7LPP) Snapdragon 865 processor in the S20, made in the TSMC foundry, the 5nm Snapdragon 888 is made using Samsung's new EUV process. The fact that Qualcomm not only switched nodes from 7nm to 5nm, but also the foundry itself , is a vote of confidence in Samsung's Extreme UltraViolet (EUV) lithography.

According to Samsung, its 5nm EUV process offers not only a fifth smaller footprint of the chipset at the same performance, but also about 20% smaller power draw. Alternatively, phone makers can choose to gain a 10% performance increase at the same battery consumption. Given that mobile chipsets are already powerful enough for anything you may throw at them, and the new X1 cores are clocked at the same 2.84GHz as the 865, Samsung is likely to go with the generous power consumption decrease.

The integrated (S21) vs standalone (S20) 5G connectivity

The 7nm vs 5nm process alone won't make a significant extra difference in battery life between the two phones, though, as the main power draw comes from the display. The phones' 5G connectivity battery draw, however, will, as maintaining a link to the 5G network is a battery hog. Why? Well, first off, before Snapdragon 888, only Huawei had integrated 5G system-on-a-chip (SoC) for flagship phones. Qualcomm made do with chipsets like the 765 in the Pixel 5 or LG Velvet, which, albeit having the 5G modem as an integral part of the chipset, are a far cry from its 8-series in terms of performance.

With Snapdragon 888, however, Qualcomm managed to finally do what it does best - pair the fastest ARM Cortex cores available with a new powerful Adreno 650 graphics AND fuse them with the X60 5G modem that is also made on the 5nm process. That alone amounts for a significant drop in power consumption when connected to a cell tower but Korean media just reported that there will also be improvements in the 5G antenna hardware.

Next-gen 5G antenna isolation

Fast 5G networks like Verizon's Ultrawide Band (UWB) mmWave can carry a lot of data at once and fast, but have very bad signal penetration that forces phone makers to slap a bunch of extra antennas all around their handsets just so that the signal can pass through your grip alone.

Samsung, however, is using the next generation of low permittivity polyimide (PI) films for the 5G antennas in the Galaxy S21 phones. This means easier signal passthrough, and less toll on the battery. 

Taken individually, all these power draw improvements, with the exception of the lower pixel density, may not amount to much, but as a whole could've provided a theoretical boost to the Galaxy S21 battery life from the same 4000mAh battery capacity. They could've, but they don't so you should expect both phones to last you about a day, and that's that.