Yes, the ebike is 12 years old. I have several identical ebikes as they were left over from a project (and have been put to good use in the intervening years). Many of the batteries have now stopped functioning (just shut down, won't charge and no LEDs lighting up), two batteries are still functioning OK and then there is this odd one on which all 5 LEDs flash. It's clearly not 'dead' like the other ones but I can't get it to function (yes, I've tried the 10 second reset).
Yes, the new 500ah replacement for £349 is a good option (I assume this is from Merlin) and I'll probably get a couple of these to keep some of the ebikes functioning (as they are still good ebikes) - the others are useful for spare parts (as the controllers, thumb switches, etc eventually stop working). I've only had one electric motor that has died.