I’m having troubles with my Victron BSC IP65 12/15 charger as it won’t stay at Bulk charge more than couple of seconds before changing to Absorption. The same happens with three different batteries (1 Li-ion, 2 lead). The lead ones have about 1A during absoption (for 4 hours) so I’m getting hardly anything in. For Li-ion Absorption gives me 10A (for 2h) so at least something is happening. I have not touched the presets and the firmware is up to date.
The charger will stay in Bulk mode until the battery voltage (measured in the charger) reaches the Absorption Voltage set.
If you think that you are getting to Absorption too early, check the Battery terminal voltage with a voltmeter. Old lead batteries tend to be sulphated, so the terminal voltage rises very quickly on charge, leading to early end to bulk. Any contact resistance in the charger leads makes this worse, particularly if spring clamps rather than bolted lugs are used.
For the lithium battery, make sure the Voltage presets of the charger are correctly set.