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Battery Life And Thermal Throttling
Battery life may be the most important performance metric for a mobile device. After all, it does not matter how quickly a phone or tablet can load webpages or how many frames per second the GPU can crank through once the battery runs down and the device shuts off. To learn more about how we test this critical facet of mobile computing, please read our battery testing methodology article.
The PCMark system test estimates battery life using real-world workloads and reflects how long a phone can last while continuously working on common tasks. The LG G4’s larger battery helps it last more than thirty minutes longer than the HTC One M9. It’s Snapdragon 808 SoC also outperforms the 810 in the M9, which experiences thermal throttling when running these relatively light workloads. Only seventeen minutes separates the remaining phones in this roundup, all of which last right around six hours.
Battery life, however, is only part of the story; we also have to take performance into account. By multiplying the PCMark battery life by the overall performance score and dividing by 1000, we get a composite metric that gives us an estimate for how much total work can be done on a single charge.
| PCMark Composite Work Score | |||||
|---|---|---|---|---|---|
| ZenFone 2 | Galaxy S6 | LG G4 | Nexus 6 | LG G3 | HTC One M9 |
| 2100 | 1930 | 1656 | 1499 | 1333 | 1306 |
Despite its smaller battery, the Galaxy S6 lasts longer and performs better than the G4, allowing you to get more total work done on a single charge. The G4 does show a 24% improvement over the G3 and also does better than the Nexus 6.
This test runs more CPU-intensive workloads and accounts for both battery life and performance. It pushes the phones hard enough that thermal throttling is a factor, making the final results a bit more difficult to interpret.
The Snapdragon 808 and 810 SoCs are manufactured using TSMC's 20nm HKMG planar process that is not a good fit for the naturally power-hungry A57 CPU cores. It’s no surprise then that we see the G4 and M9 both fall to the bottom of the chart, with the G4 trailing the G3 by 25%. The Exynos 7420 in the Galaxy S6 also uses four A57 cores, however, it’s manufactured on Samsung’s more power efficient 14nm LPE FinFET process, which gives the S6 a slight advantage here.
The GFXBench 3.0 battery test focuses on the GPU and is an indicator of battery life during intense gaming. It also effectively gauges a device’s ability to dissipate heat.
All of the latest flagship devices, including the G4, last about three hours while gaming. Our subjective gaming sessions with the G4 also predicted about a three hour limit. Both the M9 and iPhone 6 Plus run for the same length of time as the G4 but at a higher performance level. Conversely, the G3 manages to last almost an hour longer than the G4 but at a lower performance level. The Galaxy S6 throttles back to about 50% peak performance to keep from overheating, giving the G4 better performance stability over time.
The G4’s performance stability while gaming is very good. Even while running T-Rex at its onscreen QHD resolution, it does not throttle back GPU frequency until 23 minutes into the test. Performance dips to 89% of the peak value before stabilizing at 93% for the remainder of the test. This correlates well with our own gaming experience: Even after 45 minutes of gameplay, we did not notice any reduction in frame rate.
Like all plastic phones, the G4 does not fully utilize its entire surface area to dissipate heat, allowing it to build up near the motherboard. Normally this leads to excessive thermal throttling, but the G4’s Adreno 418 GPU runs cool enough to avoid this fate. The rear panel does get pretty warm but it does not exceed 120 °F, which most OEMs consider the limit where the device becomes uncomfortable to hold.
Battery life for the LG G4 is pretty good overall and comparable to other flagship devices, although the Galaxy S6 lasts longer under light workloads. Heavier workloads that fire up the A57 CPU cores such as photo and video editing, however, can drain the G4’s battery much more quickly. Having half as many A57 cores as the Snapdragon 810 should give the G4 an advantage in battery life over the HTC One M9. However, the M9, with a smaller battery, gets similar battery life as a side effect of thermal throttling. The G4 uses its A57 cores more frequently and at a higher average clock frequency, increasing power drain.
For times when you need to stretch battery life a little further, the G4 has the standard battery saver mode that you can set to kick in at 15% charge, with the option to restrict background app activity. There’s also a “Game optimizer” setting that claims to save power by adjusting the video quality in games. We ran a couple of games with this setting enabled and did not notice any difference in video quality. “Brothers in Arms 3” seemed to run with higher GPU and CPU clock frequencies when the setting was enabled, which is opposite of what we would expect. “Star Wars: Uprising,” however, seemed to run with reduced CPU frequencies when enabled. Whether the setting was enabled or not, there did not appear to be a significant difference in battery drain.
Like most flagship devices with Snapdragon SoCs, the G4 supports Qualcomm’s Quick Charge 2.0 fast charging technology. Unfortunately, the charger included with the G4 is of the 5V, 1.8A variety, which means you will need to purchase a different charger to use this feature.
