I take "never be stuck with a dead battery" to mean: You can replace individual failing cells rather than having to buy a whole new pack. By "dead" they mean "unable to be recharged". As opposed to "dead" meaning a "flat" pack that needs to be recharged.
It feels a little weird to word it like that, if I say "dead battery" or "my phone is dead", I would almost certainly mean "it is out of charge" not "it is unable to be charged"
