We got two Powerwalls last summer. As I recall, they came in a little under $10,000 each. But, there is a 30% tax credit, so that’s significant. (and no sales tax)
As to performance, we have a had a few bugs, probably stemming from a complicated home electrical situation. Overall, though, they work incredibly well. They come online instantly and seamlessly in the event of an outage. Silent, and have enough power to outlast any outage we’ve had this winter. The app is easy and informative
Oh my, does that give me a flashback! In the Good Old Days, the local NPR affiliate (KXJZ in Sacramento) aired Mick Martin’s Blues Party on Sunday afternoons. Man, what a great show!
Then it turned out the General Manager had been looting the station for a decade (https://www.capradio.org/articles/2025/01/09/golf-course-fees-fine-dining-and-college-tuition-lawsuit-claims-former-capradio-gm-stole-station-funds-to-pay-for-personal-expenses/#:~:text=Capital%20Public%20Radio%20has%20filed,%2C”%20including%20home%20improvements%2C%20family)
… and of course, the response was to lay off most of the staff, including Mick Martin. His show is now on K-ZAP (Mick Martin’s Blues Party – KZAP.ORG), but I stopped liistening to the radio since T***p started polluting the airwaves.
I think I will start listening again, a small pleasure to keep my sanity. Thanks for the memories! 
ETA: I think I get to hijack my own thread, right? 
Thank you! This is just the kind of incentive I need!
It’s pretty trivial to add a battery to a grid-tied solar system for peak-shaving / time-of-use optimization purposes (that is, the battery only ever discharges while grid power is available). Adding the ability to provide backup power to your house when the grid goes down requires extra electrical work (either an isolation/transfer switch on your entire incoming service line, or else moving all your backed-up circuits to a sub panel). I’d be pretty shocked if that $40/month option included the electrical work to support backup operation.
$40/month also just seems too low to be true. Wikipedia claims a price of $7300 for the current model, which is in the same ballpark as other battery/inverter of similar capacity (13.5 kWh). If the leasing company is able to get the 30% Residential Clean Energy Credit (in a parallel way to how car-leasing companies can take EV purchase tax credits), then the net cost to them could be about $5000 - meaning you’d have to lease the same unit for over ten years before they break even. The manufacturer warranty is only ten years, so I don’t see why anyone would keep one for longer vs. leasing a brand new one from someone else. And they company is certainly not going to be financing their purchase at 0%, so they’d be losing money over that time period.
Look very closely at the details: install costs, minimum term, termination fees (for both early and full-term), etc.
We have a backup battery for a bunch of circuits as part of our solar system. It works fine, but it was pretty expensive for what we got ($7K after tax credits for 9 kWh of capacity). It can run some lights/internet/TV and the sump pump for a day or two, but anything much more (backup forced-air propane furnace, fridges) might have it drained before the grid comes back or the sun comes out. It’s nice that it takes over for its circuits automatically and is silent, but it was definitely a lot more expensive than a gas generator, an inlet, and an interlock/transfer switch would have been.
That said, I’ve been looking at adding some more batteries since prices have come down a bit and that Residential Clean Energy Credit shaves 30% off the price. Costco had an 18 kWh EcoFlow Delta Pro Ultra for only $8k (so under $6k after sales tax and tax credit) as a Black Friday deal, but I hesitated too long 
I wonder if Sunrun maybe has some sort of power purchase agreement, on top of the equipment lease, that sells power to the OP at a margin over they’d get from the utility directly – i.e., maybe Sunrun doesn’t make the money on the equipment itself, but skim a percentage off whatever time-of-use arbitrage savings the homeowner gets?
I’m not sure about this (at all), it was just a WAG. But yeah, OP, definitely double-check and triple-check the lease terms. It’s weird that they would lease you a battery for that cheap… hard to imagine how they make money on that. Li-ion battery chemistry naturally degrades over time too, so it will be worth less at the end of your lease. It all does sound a little too-good-to-be-true ish.
Edit: Seems like that IS what they do, at least some of the time: https://old.reddit.com/r/solar/comments/y0ss8a/sunrun_power_purchase_agreement_any_good/ or PPA From Sunrun-What am I not understanding? : solar
They own the system, install it on your roof, get all the rebates and most of the solar payback, then lease it to you and sell you power at a markup. In that first reddit example, it looks like Sunrun charges the homeowner 21¢/kWh, which is more than the outright price of electricity in many areas. AND the price goes up every year.
But they also seem to offer a separate, fixed-monthly-cost option. Not sure which one the OP’s on. I guess it could still be in their favor, as long as their total monthly/annual cost is lower than what they would’ve paid to the utility. Even if it’s not as much 20-year savings as buying/financing equipment to own, it might still be a way to save money without the upfront capital? Sunrun Solar Lease Contracts: What to Watch Out For | EnergySage
But in any case, if the rest of the lease doesn’t change, seems like adding $40 for a battery backup would be a no-brainer (as long as, as you said, it actually does provide backup during outages).
Reading those Sunrun articles makes me seriously uneasy. My rule is if a deal is complicated, the corporation that put it together at scale with an army of lawyers will win and I will lose.
I personally would be a hard no on buying any house that had any sort of mandatory transfer of an agreement, be it solar lease or PPA. I suspect I’m not alone, so at least consider that before adding another legal complication that could be undesirable to buyers.
We do have solar, but I paid cash and our utility doesn’t do peak time rates and it was relatively simple to calculate the approximate break even year.
I’d consider battery backup only if I had the cash to pay for it. I don’t think it’s worth it here because power failures are pretty infrequent. That said, we did recently have a big one: a five day outage due to big storms where I would have liked to have had it. Our EV’s vehicle-to-load feature was sufficient to keep our fridge, freezers, internet, and home office working but the lack of heat got old real fast.
Thank you everyone, for the valuable information. If anyone is following this thread because they are interested in buying/leasing battery backup, here are the factors I’m considering. As always, YMMV. The basics: I have a small (<2000 sq ft) house with modest energy requirements, 27 leased solar panels that give me a small NEM balance in my favor at true-up, in the hot, sunny Sacramento Valley, with PG&E (boo!) as my provider.
Yes, these advertised “solar power for $0!!!” systems are a real rip-off. I didn’t know Sunrun was in that business, but shame on them. I have a straight monthly lease – they own and maintain the panels but I pay PG&E for power, sell excess power to PG&E, and get any NEM credits. I would not advise anyone to sign on to one of those “$0” leases – they are preying on poor people. That said, my dealings with Sunrun have always been thorough, transparent, and straightforward.
If I’d had the option to pay cash I would have, since it is much cheaper in the long run. It appears that you also don’t have to deal with PG&E, another benefit.
As @andrewm and @reply suspected, the $40/mo teaser battery that Sunrun was offering is only good if you aren’t already a customer of theirs and are buying a complete, new solar system from them. I’d also bet that if you inquire, you find out that the $40/mo rate is only good for a year or so. Loyal existing customers have to pay $150/month with an additional 3%/year built in increase.
OR I can buy a Tesla Powerwall III from them for $17900 up front, installled (net $12530 after the tax credit) with a 10 year warranty. For comparison, a reputable (i.e., not Alibaba) US company advertises a Tesla Powerwall III + Inverter or $10,500 + $500 shipping. After a 30% tax credit, that would cost about $7350, plus taxes & installation. I think given the current political climate we can expect the price of any Li batteries to increase.
A net price of $12,530 comes to about $104/mo over 10 years. With the battery, I can avoid peak pricing usage and also sign up to be a Virtual Power Plant (VPP) with PG&E. VPPs can sell power to PG&E at good rates during times when PG&E is experiencing high demand. I figure I would probably just about break even at my current usage specs. Plus I get some peace of mind, plus I don’t have to listen to my generator making a racket.
Of course Sunrun stipulates that if you connect anything to the system that was not supplied by Sunrun, you immediately void the panel lease agreement and the warranty. That means I can’t hook up the generator (which I understand can supply something called “dirty power” anyway) or even a battery I purchased from another vendor. This is another reason to buy your solar panels if you can!
Even with the Powerwall, I will probably keep my little propane-powered generator – it isn’t worth that much used – but I would plug any appliances directly into it rather than go through the electrical panel.