Tesla has begun selling an upgraded battery for its two-door Roadster, boosting the battery electric vehicle’s range by another 100 miles.

“Model S development has helped us apply new battery technology to the Roadster 3.0 packs,” a Tesla representative told us. “The cells store 31 percent more energy than the original Roadster cell. Using this new cell we have created a battery pack that delivers roughly 70 kilowatt-hours in the same package as the original battery.”

The upgrade  increases range by at least 35 percent over the sports car’s previous battery, he added. Considering the Roadster’s factory installed lithium-ion battery had a range of 245 miles, this package will extend the limit to about 400 miles. Improvements to aerodyanmics and rolling resistance, detailed here, are also included in the package.

It isn’t cheap, though. The 3.0 Battery Upgrade package costs $29,000 and requires $5,000 up front as a deposit. Included in the price is the cost of the battery and the labor to install it. Despite the high price, Tesla said it is only covering costs on the battery.

“It is not our intention to make a profit on the battery pack,” the company said. “The reason the cost per [kilowatt-hours] is higher than a Model S battery is due to the almost entirely hand-built, low-volume (only 2 or 3 per week) nature of Roadster battery packs. It also includes additional work to remove, upgrade, and reinstall the power electronics module (PEM.)”

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The batteries will be built in Fremont, Calif. at the company’s factory, with production to begin this month. They can be delivered to local Tesla service centers for installation, but with Roadsters located in 31 countries, some owners will have to be patient.

“Depending on local service team workload the upgrade will only take a few days once the parts are in place,” said Tesla. “All removed battery modules will be fully recycled or reused if possible, and we will reuse many other components from the old battery.”

Only Roadsters 2.0 or 2.5, which make up 2,000 out of the 2,500 total Roadsters built, are eligible for the upgrade. High-speed charging still won’t be an option for Roadster owners, however, as the vehicle isn’t compatible with Tesla Superchargers.