"This system has worked well for Calor gas for many years."
No doubt, Mr AC.
But gas tanks don't have a memory of how fast (or slow) they were charged or discharged.
So have you picked up one that's only ever been overnight charged and discharged gently? Or was some "boy racer" sales type who simply must get to their next meeting ASAP and only ever uses a fast charger? You don't know, although "smart battery" tech could flag if a battery pack is on its last legs and need to junked.