Carmaker Nissan has announced a rival to Tesla's Powerwall home battery pack called the xStorage. Like other residential batteries, the device is supposed to pull cheap electricity off the grid during off-peak hours and feed it back into the home when power is in demand and expensive. You can hook it up to renewable energy resources to charge it up off-grid, and Nissan says a companion app will help owners easily monitor usage.

The xStorage is on sale in Europe only, and Nissan reportedly has no immediate plans to bring it to the US. Prices start at €4,000 ($4,560) for a 4.2 kWh model, which includes installation. By comparison, Tesla's 6.4 kWh Powerwall costs $3,000, but that doesn't cover installation and extras. (These raise the total cost to $5,000, according to The Financial Times.) Carmaker Mercedes has also announced plans to sell its own residential batteries (2.5 kWh each, combinable in groups of up to eight), but hasn't confirmed pricing.

This clutch of launches and unveilings shows the interest in the home battery market, but it's still not clear whether these devices make enough economic sense to capture a broad audience. The battery packs listed above aren't big enough to power a whole house through extended power outages, and will usually take years for owners to recoup the cost (this time period may shorten if a home-owner has alternate energy sources like solar panels, but then these cost too). Still, companies obviously believe there's potential here, and more products will only help develop the market and lower prices.