Instead, it is for a sleek battery the size of a mini-fridge that will allow homeowners to take better advantage of the energy their solar power systems produce, whether to cut costs or to maintain a steady source of electricity during power failures. Vivint will start selling the Mercedes home batteries to new customers only in California in the second quarter of this year. Tesla’s $5,500 Powerwall 2 has a 13.5kWh capacity, and customers can buy up to 10 of those to scale to their needs. Vivint’s offerings will be cheaper, though. The company plans to sell a basic package of a 2.5kWh for $5,000 when paired with solar panels, while the complete 20kWh system will run around $13,000, including installation.