Given the weight + hazardous materials in an AGM, I can't see shipping hitting $15/unit unless you're talking about a container full.
I think you're missing a lot of costs beyond the raw materials...
As for reputable warranties against breakdowns, please check out the fine print of the Powerwall warranty terms and conditions. It's a '10 year warranty' with some very special legalese baked inside that may make you reconsider the cost premium commanded by guarantees provided by a company very adept at lawyering up and navigating regulation.
The warranty (at least in North America) has provisions for voiding warranty claims in off-grid scenarios: during the entire period from installation to claim you must have constant access to the Internet for remote updates. If Tesla detects you go offline, they reserve the right to deny your claim.
In addition, if you use the Powerwall for additional applications besides self-consumption of solar power, you're capped at 18 MWh aggregate throughput before the claim is denied. Consider a 6 KWh solar installation for 5 hours daily charging, with the purpose of selling back energy to the grid (not classified as self-consumption). Now also realize that since this is aggregate throughput, all the charging, smoothing, and then discharging to the grid takes 2x the throughput. How many days warranty do you end up getting from this '10 year warranty'? 18 MWh / (6 KWh * 5 * 2) = _300 days_.
Finally, the warranty specifically says how they may choose your compensation. Could be an outdated refurbished model, but could also be cash market value of a similar system at the date of claim. Given the exponential rate of dwindling costs for energy storage, that's a gamble that in a few years your warranty may just pay out a tiny fraction of what you originally invested in you were sold a lemon.
Tying the luxury price premium to guarantees feels very reminiscent of smartphone insurance... which is almost never a good buy. I'm with parent, let's just be honest here: you're paying for luxury markup -- sexy compact design and a good story.
Regarding costs: I didn't factor in every possible cost but I still find it hard to believe that these high powered lithium batteries will work out to be cheaper than AGM batteries at this stage -- even factoring in things like shipping and installation costs (though I may be wrong about this, I think that this battery is likely to be like the Apple of PC components.)
By the way: If anyone is interested in suppliers have a look at companies like Guangzhou Henda Power Ltd and Guangzhou ESG New Energy Technology Co. They sell cheap AGM batteries like the ones I've mentioned. And you may even bump into one of SolarCity's suppliers if you do enough research ;)
Anyway, thanks for the downvotes for not band wagoning but none of you have any clue what you're doing.
Edit: Though we only need 5 of them, not 9. The whole point of deep cycle batteries is that it's OK to discharge the quoted capacity every cycle.
Lets proceed with these calculations and say that you also want a good quality "grid-tie" "pure sine wave" inverter (to feed your stored energy back to your home grid) which will set you back any where from $100 - $1000. Your total cost for energy storage is still only going to be around $1180 (worse case.) Now consider that the life time for the Tesla batteries and standard AGM batteries seem to be very similar and I honestly have no idea what the customer is actually paying for.
Is the compact size and sleek appearance really worth the extra cost to the customer? Maybe it is. Maybe people don’t want to have a nerdy battery bank in their homes but to me the benefits all seem a little petty. (Granted, I definitely do see the benefit for tech like this in electric cars though, don’t get me wrong.)