They can appear to charge ok, but won't start the car after a short period of inactivity - it can be as short as overnight. Its like there is a mysterious power drain in the car, but its just the battery's internal resistance and it self-discharges. My CTek refuses to charge the two I have though - it does its load test and gives up. BR sits on the CTek when she's in the workshop and still seems to be ok, but I have Tayna Batteries on speed dial for a Varta when the Yuasa dies
Knowing BR, it'll be on a trip to Tesco of course
There are a few reasons why a lead acid battery can do this - only Yuasa would be able to tell for sure by taking one apart. Trickle charging helps with sulphation, but I'm not sure whether its that or something else. On all the dead ones I've seen, they still show the green health / charge indicator too which is bizarre.