The climbing rapidly was when in bulk mode ( constant current) on the victron charger. It quickly rose to 13.8v then switched to absorption at a (constant voltage) 13.8v.
It climbs rapidly from 13.2V to 13.8V at 10Amps CC (tens of minutes?) then spends hours at 2Amps before going to "float". If it was charging at 2Amps for say 4 hours that is 8AH at which the battery should be at ~95% SOC. That means to me that the battery was somewhere around 87% before it switched to absorption.
Tens of minutes at 10Amps is still not many AH.