Tesla's not-so-secret plan to fill the world's homes with giant batteries could involve leasing them, according to a report from The Guardian. The batteries have apparently already been leased to customers of SolarCity, a renewable energy firm chaired by Tesla CEO Elon Musk, as part of a small pilot program. Customers were asked to finance a $1,500 downpayment followed by $15 monthly payments for 10 years. The puts the overall cost of a 10-year lease at $3,300, or $27.50 per month. According to the report, the cost is further reduced by subsidies from energy companies, who support the idea as it reduces the load on their networks during peak hours.