Perhaps an old timer who knows lead acid batteries can help:
This is from my SMA installation manual:
• Select the parameter Time for boost charge of battery / 222.02 AptTmBoost and set to the boostcharge absorption time recommended by the battery manufacturer.
• Select the parameter Cell charge setpoint voltage for boost charge / 222.07 ChrgVtgBoost and set it to the cell-voltage setpoint recommended by the battery manufacturer for boost charge.
I’m going to guess this is a bad translation, since SMA is German.
Boost Charging translates to Schnellladen, which could also be Fast Charging, but I am going to guess they mean Bulk, so this is either the bulk timeout or the max absorption time.
The text from one of the SunnyIsland manuals says:
13.5.1 Boost Charge
The boost charge is the most common charging process of the Sunny Island. The boost charge ensures a high generator workload through a high charging voltage over a short period of time. With liquid FLA lead-acid batteries, this charge process should be used for gassing and thus compensating the electrolytes. The boost charge process can charge the battery up to approx. 85% to 90%.
That’s the definition of bulk charging, ie the constant current phase before we reach the absorption voltage.
The timeout is more ambiguous. It could either be what Victron calls the Bulk timeout (a safety setting that backs off if the battery voltage won’t rise within that time), or it could be the time to hold the battery at the absorption voltage. I think it is the second one, because it talks about “absorption time recommended by the manufacturer”.