Apple (NASDAQ:AAPL) Watch's battery will only last around 19 hours on "mixed" active and passive use, according to a recent 9to5Mac report. The report also claims that the device will last two to three days on standby or power-saving modes. Those numbers back CEO Tim Cook's previous statement that users would need to charge the watch daily, but they might disappoint consumers who hoped that Apple would improve the watch's battery life before its launch.

Source: Apple.

Apple Watch expectations are currently all over the map, from 10 million units (Piper Jaffray) to 60 million units (Morgan Stanley) within the first year, so we should consider whether or not a merely average battery life could impact sales.

Bridging the battery life gap
Three common complaints about smartwatches are their lack of aesthetic appeal, underwhelming health-tracking features, and weak battery life.

Apple Watch arguably addresses the first two issues, with high-end watch bands and its HealthKit platform, but a single day battery life would merely be comparable to Samsung's (NASDAQOTH: SSNLF) Gear smartwatches. Samsung's 3G-enabled Gear S lasts for one to two days, while the spartan Gear Fit lasts three to four days.

Meanwhile, smartwatches with black-and-white LCD and e-ink displays, fewer power-hungry apps, and less biometric sensors last longer. For example, Pebble's smartwatches last for a week on a single charge. Cheaper fitness bands which use lights instead of displays -- like Misfit's Shine and Flash -- last for months on a single battery.

New smartwatches, which bridge the gap between Gear and Pebble smartwatches, are also hitting the market. Lenovo's (OTC:LNVG.Y) new $90 e-ink watch, the Vibe Band VB10, tracks user activity, receives notifications, and last a solid week without charging.

Lenovo's VB10. Source: Lenovo.

Not as simple as it seems
Although it seems like smartwatches like the Vibe Band could threaten the Apple Watch with similar features and superior battery life, the definition of "good" battery life varies greatly from device to device.

A survey from Fixya last May revealed that 10% of surveyed Galaxy Gear owners were unhappy with the device's one day battery life, yet 10% of Pebble owners were still dissatisfied with the device's one week charge. This means that consumers are equally forgiving of powerful devices with lower battery life and less powerful ones which last longer. Moreover, Samsung controlled 71% of the smartwatch market at the beginning of 2014, according to Strategy Analytics, although none of those smartwatches lasted near a week.

Those two figures indicate that new features could actually be a stronger deciding factor in new smartwatch purchases than battery life -- which would be good news for Apple.

Why battery life still matters
However, the need for daily charging might upset Apple's HealthKit plans. One of HealthKit's goals is to synchronize biometric data from Apple Watch to the Health app on iOS 8, which is then transferred to a patient's electronic health record (EHR). A direct connection between a user's wrist and the hospital's EHR would benefit from round-the-clock biometric monitoring which isn't disrupted by nightly charging.

By comparison, Samsung's Simband, a reference design for a "modular smartwatch," has room for a removable battery which can be swapped out and recharged. Therefore, smartwatches developed under the Simband design and synchronized to SAMI (the company's equivalent of HealthKit) can possibly provide a more accurate long-term snapshot of a user's health. Since Simband is also designed to be customized by biometric sensors from third-party developers, it might eventually evolve into a better health-tracking wearable platform than the Apple Watch.

Samsung's Simband. Source: Samsung.

Active versus passive use
Apple Watch's 19 hours of "mixed use" reportedly only include 2.5 to 4 hours of actively using apps. This means that playing a game or using messaging apps for extended periods of time could quickly wear down the battery. This might mean trouble for app developers looking toward Apple Watch as the next big mobile gaming platform.

Electronic Arts (NASDAQ:EA) previously expressed interest in developing Apple Watch games. Many of EA's mobile games depend on periodically checking back on completed tasks and energy refills, but games built on the same concept might not work if Apple Watches can only be used "actively" for 2.5 hours daily.

Competing for a small market
Market projections for the overall smartwatch market remain high. Research firm ON World expects smartwatch shipments to soar from 4 million units in 2013 to a whopping 330 million in 2018. However, a recent Fortune-Survey Monkey survey revealed that a mere 12% of consumers were "extremely" or "very likely" to buy a fitness band or smartwatch in 2015.

Therefore, the actual reception for Apple Watch might actually be more muted than analysts expect. Weak battery life probably won't sink the Apple Watch, since Samsung has sold plenty of devices with comparable batteries, but it could fail to win over consumers who prefer longer lasting e-ink watches and fitness bands.