Victron energy Skylla-i 24/80 1+1 Mode D'emploi page 6

Figure 3 Location of battery connections:
two output models
Note:
The starter battery can draw current from the battery connected to the main battery terminals in case the starter battery voltage is
lower than the main battery voltage. However, the main battery cannot draw current from the starter battery even when the starter
battery is fully charged and the main battery is at minimum charge level.
Figure 4 Location of battery connections:
three output models
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+: Main battery plus
-: Main battery minus
Starter battery plus
Triple output model
connections
+A: Battery A plus
+B: Battery B plus
+C: Battery C plus
-: Battery A/B/C minus