The battery is NOT guaranteed to DIE in 5 years!! or turn into shit just because it's now 7 years old. If you treat it properly and don't continually push either end of the charge boundries, it should last a very long time and keep you happy.
Also remember, tech.. gets better and cheaper as time goes on as well... generally. Lithium prices have come down a LOT just over the past few years. Batteries that were 2k now you can get for 750 dollars. solar panels started out 3 dollars a watt, now are 25 cents a watt, even with todays high prices!
My point being, even when it IS time to change out the battery, there may be a good chance you can get a newer one, newer tech, maybe cheaper, faster, bigger, better type thing.
The industry is maturing pretty well here and everyone knows the next major milestone is going to be the storage system. aka battery / cap system, so many are working very hard on this very problem, because face it,. the first to come out with a game changing alternative, just like Lithium was the game changer over lead acid, is poised to make BILLIONS, literally overnight in this one.
Aaron