We are NOT anywhere close to the theoretical limits.
For a lithium-ion battery – the theoretical limit is 460 Wh/kg. Tesla batteries are at 250 Wh/kg.
So – we still have close to a 100% improvement possibility.
But that assumes we stick with Lithium ion technology.
Lithium Copper Chloride batteries can theoretically reach 1,200 Wh/kg and Vanadium Boride Air batteries can reach 27,000 Wh/kg…which is 100 times better than a Tesla battery pack.
Tesla’s new Roadster will have a 600 mile range…with Vanadium Boride Air – they could go 60,000 miles!!
Unfortunately, the Vanadium Boride Air batteries are not (currently) rechargeable…but if you can get 60,000 miles from a battery without ever recharging it – you might well decide to throw it away and stick a new one in there every 60,000 miles.
Providing we can recycle them efficiently – that may just be the right solution!
But battery technology is still changing – we don’t know what the real limit might be.
Cost limits are another matter. The current cost of batteries is down to production methods.
A Tesla battery pack with about 4,000 individual batteries in it costs about $3,000 to replace. So less than $1 per battery. If you wanted to buy one of those batteries from some no-name place in China – you’d pay about $8 for them.
So quite possibly, Tesla’s advanced battery manufacturing plant is doing things *WAY* more efficiently.
More efficiencies are probably possible yet…who knows?
But your claim that we at the limits is clearly untrue.