Competition is heating up in the race to install home battery systems, with heavy hitters and nimble startups all vying for a piece of the market. Tesla may have led the pack for years, but recently it has been feeling the heat from upstarts like Base Power, which has raised $2 billion in less than a year. The automaker-cum-energy company recently introduced a new Powerwall battery leasing plan that cuts the monthly price by more than two-thirds, an apparent response to all that competition. Jus...