Tesla has released the warranty for the DC version of the Powerwall 2. The warranty for the AC version has not yet been released, but I think it is a safe bet to assume it will basically be the same.
The warranty is a large improvement over the one for the original Powerwall. When cycled once per day the Powerwall 2 has the lowest cost per warrantied kilowatt-hour of any battery system by a large margin.
But for many households, the Powerwall 2 warranty is likely to last for under 9 years rather than the full 10 years I was expecting.
Length Of Powerwall 2 Warranty When Cycled Once Per Day
The Powerwall 2 warranty has two categories. The first is for people who only charge it off solar power. In this case the warranty  lasts for 10 years and has unlimited cycles. Unlimited cycles sounds wonderful, and it certainly isn’t bad, but only charging off solar means people who are on-grid and have time-of-use tariffs won’t be able to charge it using low cost off-peak grid electricity, while people who are off-grid won’t be able to charge it using a generator. Because of these limitations, most people are likely to fall into the second warranty category.
The second category allows a Powerwall 2 to be charged off things other than solar, but the warranty is limited to 10 years or a total of 37,800 kilowatt-hours of stored electricity – whichever comes first.
If the battery was cycled once per day and its capacity never deteriorated from when it was new, the warranty would be over in 7 years and 8 months. Unfortunately, all lithium-ion batteries deteriorate with use and over time even if they’re not used.
The warranty promises they will still have at least 70% of their capacity left by its end, whether it is 10 years or 37,800 kilowatt-hours. If we assume the average battery will have 75% of its original capacity by the time its warranty is finished and that deterioration happens at a constant rate, then the warranty will last a little over 8 years and 9 months when cycled once per day.
If a Powerwall 2 is cycled at a different rate, the following graph shows how long the warranty can be expected to last. In the unlikely event it is cycled twice a day it will only last 4 years, while if it is cycled 0.8 times a day it will last a full 10 years.
Finn Peacock is Founder & CEO at SolarQuotes
