I'm not so sure that would be anything but marketing spiel as even the highest quality battery can't circumvent the facts of chemistry. The battery will have a finite number of charge cycles and after that it will degrade, even the best batteries only last for around 1000 charge/discharge cycles before suffering significant degradation.
It's more the number of weeks the thing is supposed to be able to 'last' in stand-by, without bleeping at me to tell me to stick it on charge, rather than how many years use it might survive.
Was actually a significant sales feature for me buying it, given how oft I put the old one down with my keys, then had some-one banging on the door yelling
"Why dont you ever answer your bludy PHONE!", followed by a flury of smart-phone swiping, and
"I Cant Hear it!" and tornado of scattered mail, and dining condiments, as they try and find where I might have dumped it, concluding with
"I dont know, now.. I've forgot" when I ask,
"What did you want me for anyway?" as the notion that they have come round, and can actually talk to me face to face, and they don't actually NEED a telephone (if they ever did!, given most likely is my next-door-but-one neighbour, we can usually hear yelling at the dog three counties away!), causes a mental aberration... in the idea of actually NOT using a telephone to talk to some-one! Hey, that Neighbor? Yes, not only does she use phone to talk to her kids in the bedroom from the kitchen, she even uses it to talk, well, txt them across the ruddy living room!!!