Battery

A battery is a device that stores chemical energy and converts it to electrical energy to power an electronic device. In virtual reality (VR) and augmented reality (AR), the battery is the component that lets a head-mounted display or pair of smart glasses run without a wall cable, and its capacity, weight and heat output are among the main constraints on the design of self-contained ("standalone") headsets. Almost every standalone VR headset and AR device shipped since the late 2010s uses a rechargeable lithium-ion (Li-ion) or lithium-polymer (Li-po) battery, the same chemistry used in phones and laptops.

Battery capacity is usually quoted two ways: in milliampere-hours (mAh), which describes charge at a given voltage, and in watt-hours (Wh), which describes energy and is the more directly comparable figure across devices. A typical standalone VR headset carries roughly 19 Wh of battery and runs for about two to three hours; smart glasses carry well under 1 Wh and run for a few hours of mixed use. Because the battery is heavy and generates heat alongside the processor, headset makers either build it into the front of the device, move it to the back of the head strap for balance, or place it in a separate pack worn on the body.

How a lithium-ion battery works

According to the United States Department of Energy, a lithium-ion cell is built from an anode and a cathode (which store the lithium), a separator that blocks the flow of electrons inside the cell, an electrolyte that carries positively charged lithium ions between the two electrodes, and positive and negative current collectors. During discharge the anode releases lithium ions to the cathode, which generates a flow of electrons through the external circuit that powers the device; during charging the process reverses and lithium ions move back from the cathode to the anode. The Department of Energy lists the technology's advantages as light weight, high energy density (the amount of energy stored relative to mass) and the ability to recharge.

Energy density is the figure that matters most for wearable computers, because it sets how much runtime can be packed into a given weight. Current lithium-ion cells store on the order of 200 to 300 Wh per kilogram at the cell level, with high-nickel cathode chemistries such as NMC811 reaching roughly 250 to 280 Wh/kg.

Lithium-polymer cells, which use a gel or solid polymer electrolyte rather than a liquid one, are a variant of the same lithium-ion chemistry. They can be made in thin, flat or curved shapes, which is why they appear in slim headsets and in the curved rear-mounted packs of some VR devices.

History

The lithium-ion battery was developed over roughly two decades by three researchers who shared the 2019 Nobel Prize in Chemistry: M. Stanley Whittingham, John B. Goodenough and Akira Yoshino. In the early 1970s Whittingham discovered how to store lithium ions within the layers of a disulfide material; in 1980 Goodenough found that lithium cobalt oxide made a far more stable, higher-voltage cathode; and in the early-to-mid 1980s Yoshino assembled the first practical cell by pairing Goodenough's cathode with a carbon anode based on petroleum coke. Sony brought the first commercial rechargeable lithium-ion battery to market in 1991, which made small, long-running portable electronics possible.

That chemistry is the direct ancestor of the cells used in VR and AR hardware. The shift from tethered, externally powered headsets to battery-powered standalone devices in the late 2010s depended on lithium-ion energy density improving enough, and on mobile processors becoming efficient enough, to run a headset for a usable session on a battery light enough to wear.

Battery in VR and AR hardware

A VR or AR device's runtime is set by the ratio of how much energy the battery holds to how fast the device draws power. The display, the tracking cameras, the radios and especially the system-on-chip all draw current, and mixed-reality passthrough, which keeps the cameras and full-color displays running continuously, is one of the most power-hungry modes. The processor's efficiency therefore directly affects battery life: Qualcomm states that the Snapdragon XR2 Gen 2 used in the Meta Quest 3, built on a 4 nm process, delivers about 2.5 times the peak GPU performance of the previous generation with roughly 50 percent better power efficiency.

Battery placement and weight

Because a battery large enough to power a headset is heavy, where it sits affects comfort as much as runtime. There are three common approaches.

The Meta Quest 3 integrates its battery into the front of the headset, next to the displays and processor. iFixit's teardown found the cell behind roughly 50 screws, several coaxial cables, a heatsink and the mainboard, and noted that Meta sells no official replacement part; iFixit gave the headset a provisional repairability score of 4 out of 10. Putting the battery up front adds to the device's front-heavy balance, a tradeoff GSMArena's review noted when describing the extra weight being felt during rapid head movement.

The Meta Quest Pro instead places a curved-cell battery in the back of its head strap. The curve lets the cell contour to the head, and the rear position counterbalances the optics at the front for better weight distribution; Meta rates the headset at one to two hours per charge and ships it with a 45 W dock that fully recharges it in about two hours.

The Apple Vision Pro moves the battery off the head entirely into a separate silver pack connected by a cable. The pack attaches to the headset with a proprietary connector that locks with a quarter turn and charges over USB-C. This keeps weight off the face but tethers the wearer to a pocket-sized pack, and because there is no reserve cell inside the headset, disconnecting the pack immediately powers the Vision Pro off, so swapping to a second pack requires a full restart rather than a seamless hot swap.

Capacities and runtimes

The table below lists battery figures for several VR and AR devices as reported by their makers or by teardowns. Where a manufacturer has not published a capacity, the value is marked as not disclosed.

Device	Battery capacity	Rated runtime	Battery location	Charging
Meta Quest 3	About 4,985 mAh (19.44 Wh) lithium-ion	2 to 3 hours; less under heavy mixed reality	Front of headset	18 W, about 2 hours to full
Meta Quest Pro	Not disclosed (curved cell)	1 to 2 hours	Back of head strap	45 W dock, about 2 hours to full
Apple Vision Pro	External pack rated at 35.9 Wh	Up to 2.5 hours general use; up to 3 hours video	Tethered body-worn pack	40 W adapter; usable while charging
Ray-Ban Meta (Gen 2) glasses	About 154 mAh	Up to 8 hours typical use	In the temple arms	Charging case adds 48 hours; 50% in 20 minutes

The Vision Pro's 35.9 Wh pack is roughly the energy of a 10,000 mAh phone power bank, but it powers a far more demanding device, which is why its rated runtime is close to that of headsets with much smaller batteries. Apple lists 2.5 hours of general use, 3 hours of video playback, and notes the device can be used while charging.

Smart glasses sit at the opposite end of the scale. The first-generation Ray-Ban Meta glasses ran a few hours, and Meta said the Gen 2 model announced on 17 September 2025 lasts up to eight hours of typical use, about double the first generation, with the folding charging case providing an additional 48 hours and a fast charge reaching 50 percent in 20 minutes. The cell inside each pair is only around 154 mAh, a constraint set by the size and weight of an ordinary eyeglasses frame.

Charging and accessory batteries

Most standalone headsets charge over USB-C, and many ship with or accept a dock so the headset and controllers recharge between sessions, as with the Quest Pro's 45 W dock. Because a built-in battery cannot be changed without disassembly, a market of third-party battery straps has grown around the Meta Quest 3 and Meta Quest 3S. These replace the standard head strap with one containing a rear battery pack, both extending runtime and shifting weight to the back of the head. Some, such as BOBOVR's hot-swappable strap systems, use a magnetic quick-release so a depleted pack can be exchanged for a charged one without removing the headset or interrupting the session, an external version of the hot swap that the headsets themselves do not support.

Power as a design constraint

Battery energy, device weight and heat are linked tradeoffs in headset design. A larger battery adds runtime but also mass, and lithium-ion chemistry has improved only incrementally, so designers cannot simply add capacity without making the device heavier and hotter. The processor is downclocked to stay within a thermal and battery budget that depends on how much weight the headset can carry: a heavier headset can fit a larger heatsink and run faster, but is less comfortable to wear. This is one reason standalone headsets use mobile-class chips such as the Qualcomm Snapdragon XR2 family rather than the far more power-hungry desktop hardware used by PC-tethered headsets, and why mixed-reality passthrough, which runs cameras and displays continuously, noticeably shortens runtime.

Lithium-ion cells also age. Capacity fades over hundreds of charge cycles, and both elevated temperature and a high state of charge accelerate that loss, so a headset rated for two to three hours when new will deliver less after a year or two of heavy use. Because headsets generate heat next to the battery and are sometimes used in warm rooms, thermal management protects both performance and long-term battery life.