I think the older 2018 manual is way more clearer.
The 2019 manual says "one after the other up to 80-90%"... it does leave it open for interpretation whether or not they actually alternates charging in 5% intervals or not. Judging for the old manual, the Intuvia display that displays both batteries and alternates flashing between the two, and my observations what happens if you interrupt charging mid-time is that it clearly charges in 5% intervals up to the "80-90%" level.
The 2019 manual says "one after the other up to 80-90%"... it does leave it open for interpretation whether or not they actually alternates charging in 5% intervals or not. Judging for the old manual, the Intuvia display that displays both batteries and alternates flashing between the two, and my observations what happens if you interrupt charging mid-time is that it clearly charges in 5% intervals up to the "80-90%" level.