Well, the Powerwall 1 was introduced back in April 2015 for a price of $3,000, which is $3,953 in 2024 dollars. The specs said a total of 6.4 kWh with a continuous and peak charge/discharge of 3.3 kW. The inverter was separate, because it was designed to be integrated into an existing solar setup.
The Powerwall 3 was introduced in September 2023 for $7,300 but includes an integrated solar inverter. The specs for it are double the total power at 13.5 kWh, with a continuous charge/discharge of 11.5 kW -- more than triple the original -- and a peak, 10 second draw of 30 kW, about 9 times the original.
So, we're talking more than 3x the device, plus a solar inverter, for less than double the price. Oh, and the original used nickel-manganese-cobalt batteries that were only rated for 5,000 cycles in the warranty. Battery chemistry is now Lithium-Ferrous (Iron)-Phosphate, which is more stable than the NMC and the warranty reflects that at 10-year, unlimited cycles. Oh, and the 3 is expandable with separate "DC packs". That's just batteries without the inverter.
As far as EV replacement batteries, there's a decent market for Nissan Leaf aftermarket batteries. The official, 24 kWh Nissan replacement is $5,500 + install. Third party depends on the current demand, but averaged half that when I last checked and there were even upgrade options (bigger batteries) if you wanted to pimp out your Leaf.
So... yes, batteries are getting substantially cheaper and while the end user may not be seeing the full 90% decrease, we're seeing quite a bit. That full cost decrease is for utility scale buyers.