That represents a substantial gain on alternatives that can struggle to run longer than a day.
The Geak Watch 2 models achieve the feat by using a hybrid screen that switches between a "high definition" LCD colour display and a "standby mode" battery-saving e-ink one.
One expert said this was "very clever".
"One of the big challenges that smartwatch manufacturers have had is that people stop using the devices, and one of the reasons they do so is that they have to be charged on a regular basis, whereby they are being taken off constantly," said Ben Wood from the tech consultancy CCS Insight.The basic version features a plastic bezel, while the Pro model has a metal one
"Anything that enhances the battery life is a big win.
"That's why we've seen people who have Pebble devices typically using them longer than some of the rivals with daily charging requirements."
Pebble smartwatches also promise "up to seven days" between charges thanks to the use of a black-and-white e-paper display, but lack the ability to switch to a colour LCD screen or run Android, restricting the amount of apps they offer.Two models
The new smartwatches are made by Shanda, a Shanghai-based company that helped pioneer the sector with its first Geak Watch in 2013.The Geak Watch 2 models feature both an LCD display and an e-ink one
Reviews at the time indicated that the first-generation device lasted between 10 and 15 hours.
Early adopters are being rewarded with an offer to trade in the old watch for a free new one.
Shanda says:the basic Geak Watch 2 lasts six days on a single charge with normal use or 15 days if restricted to standby mode. It costs 1,999 yuan ($327, £203) the Geak Watch 2 Pro lasts seven days with normal use or 18 days if kept in standby mode. It costs 2,499 yuan ($409, £254).
Owners can alternate between the two display modes by pressing a power button.LG's G Watch R lacks the e-ink screen, but is available outside China
Both watches feature a circular 1.3in (3.2cm) display offering a resolution of 254 pixels per inch when the LCD is in use - roughly the same specifications as LG's G Watch R, which does not include the e-ink component.
Shanda's Pro model features a metal, rather than plastic, bezel and also includes a built-in heart rate monitor.
The models are powered by Geak Watch OS, a proprietary "skinned" version of Android 4.3 that has its own app store and user interface, rather than Google's Android Wear software.
This helps it overcome the fact that Google Now - the anticipatory search service that provides much of Android Wear's functionality - is blocked in China, where the Geak devices are sold.Price erosion
Mr Wood said it was not yet clear whether the hybrid screens matched existing watches in terms of display quality, but said that if they did other companies might follow with similar products made available worldwide.
"We're seeing a tremendous amount of innovation in wearables coming out of China," he said.
"It's amazing how all of the different manufacturers quickly follow successful ideas.
"But China is not only the epicentre for innovation, it's also the source of extreme price erosion, which is making things challenging for the established players."Tim Cook has indicated Apple's Watch must be charged at least once a day
Samsung, LG, Motorola, Sony and Asus are among other companies to offer smartwatches that typically last about a day per charge.
Many analysts have speculated that Apple's Watch - a smartwatch to be released in 2015 - would boost sales across the sector.
But there has been concern about Apple's admission that battery life will be constrained.
"I think given my own experience, and others around it, that you're going to wind up charging it every day because you're going to use it so much," Apple's chief executive Tim Cook said at the WSJD Live conference, according to a transcript by the Verge news site.Long-life LCDs
While improvements in the efficiency of computer processors are helping compensate for the relatively slow pace of battery tech advances, they can go only so far.
But research elsewhere in China might offer an alternative to falling back on e-ink.
Researchers at Hong Kong University of Science and Technology have reported that they have created a new type of LCD screen that can hold a static image for years without requiring power.
This could be suited to smartwatches that change only a single digit every minute to show the time when not running more complex apps.