Researchers in China have developed a water-based battery, which is claimed to be much safer and energy-efficient than “highly flammable” non-aqueous lithium batteries.

Interesting Engineering | Nature Energy Paper

Resolves YES if a top 5 smartphone brand by market share is available on sale with an aqueous battery in any part of it's composition.

Top 5 brands by market share are currently Samsung, Apple, Xiaomi, Oppo and Vivo, but I will re-review this when relevant. This restriction is to rule out hobbyists or other small-run shops pushing out something that may technically meet the criteria but is not widely available to verify aqueous battery claims.

The phone must be on sale, not just up for pre-order, and in shops and not just a paper launch, before January 1st 2028.

This market tracks whether such a phone will launch and be tested, if it is removed from sale or becomes otherwise unavailable, this market still resolves YES as long as it can be verified to have been sold and have contained an aqueous battery.

An aqueous battery must be a component of the phone and not the manufacturing process.