Does it have a guaranteed life-time of use (e.g. 500 charges, then discard)??? Thank you.

Rechargeable products like this are generally designed for repeated everyday use over a long period.

That said, as with any electric heating product, the practical life will depend on how it’s used and cared for (avoiding damage to the cable, not sitting on or crushing it, following the instructions, etc.), and internal components can eventually wear out over time rather than at a fixed, pre‑set number of charges.