In Japan there is already a company that has designed and implemented the hardware to take a certain brand of used vehicle batteries, stack them in a storage container and use them as storage at solar farms so they can sell power when it fetches the best price rather than being constrained to only being able to sell power when the sun is up.
But that is the problem. It's an artificial way to distort supply and demand, and inflate price, or cost to consumers. Sadly, it's UK government policy, ie constraint payments means millions get given to renewable producers to not supply electricity when there's no demand. Those costs are passed through to consumers via their electricty bills, which then increases energy poverty. Or the cost to businesses, who may decide to relocate production to somewhere where energy costs are lower. Or just increase prices. It's also not novel, ie battery backups or other historical solutions to energy storage like Dinorwyg.
Without subsidies or a rigged market, nobody but off-grid users would buy this energy given it's typically 3-4x the cost of alternatives like gas or nuclear.. And of course because renewables are unreliable and intermittent, you need gas turbines as well for backup.
I have seen other startups that do the same to turn used Prius batteries into home storage batteries.
It shouldn't, but it probably will. There are quite a few YT videos showing people doing this though. Which is also a problem for Tesla. So Tesla's get written off regularly for minor damage due to high repair costs. People buy the cars, strip the battery packs and resell them cannibalising the Powerwall business. Plus adding risks, ie if battery elements are defective, or charging/cooling systems, then there's a risk of fires which aren't easily extinguished. Which can also be a problem with domestic solar installs. If they're done badly and you end up with DC arcs, you may have rooftop fires that do a lot of damage. So warranting and liability issues may mean start-ups get shut down fairly swiftly.