Samsung pushed an over-the-air (OTA) software update for the Exynos-based variant of the Galaxy S4 (GT-I9500), which addresses two glaring bugs that came to light after last week's big update that gave it Android 4.3, KNOX, and Galaxy Gear support.
Pushed as a "system stability" update (the only item on its change-log), the 10-odd megabyte OTA update appears to have fixed the rapid battery drain issue noted on our Galaxy S4 GT-I9500; and jerkiness with the user interface. The user-interface feels smoother to coast through after the update.
The older Android 4.3 update apparently came with a narrower safe voltage range value for the GT-I9500's 2,600 mAh battery, which translated to nearly half the normal usage. A smartphone measures battery by monitoring its voltage. Its electronics can function only within a safe voltage range. The narrower that is, the lesser power is yielded from the battery, before a recharge is forced upon the user.