Good condition battery flat after 9 days

Good condition battery flat after 9 days

My battery is in good condition according to my Oxford trickle charger, yet the bike was parked up for 9 days while I was away and the battery is dead. Only enough charge to barely get the indicators working but not enough to turn over the bike.

Any ideas what the problem could be, I have no alarm but do have an immobiliser?
It’s a proper pain getting the battery in/out. 😮

Source: Good condition battery flat after 9 days