Compatibility between v3 and v4
The main difference between v3 and v4 is the new battery system. While v3 worked with Pb and optinal NiMH accumulators charged by an electronic curcuit inside Robotino (located directly behind the batteries) v4 uses Li-Ion batteries from Festool.
Because the voltage of the Pb/NiMH batteries in v3 can be higher than the 24V of the external power supply, the batteries must be disconnected from the system to ensure that power comes from the external power supply and not discharging the batteries even if an external power supply is attached.
In v4 this behaviour of disconnecting batteries from the system whenever an external power supply is connected is not necessary any more. The 24V of the external power supply are much higher than the maximum reachable battery voltage of the Li-Ion batteries. Therefor the batteries stay connected to the system so that both external power supply and batteries can power the system. This is useful if the external power supply can only deliver a limited amount of current. If the system's power consumption exeeds the power of the external supply the batteries can fill the gap.
On boards starting from mid 2019 there is a jumper JP13. Keep JP13 open if you are using the CPU board with a Robotino v4 chassis. Close JP13 if you are using a Robotino v3 chassis.
If there is no JP13 you have to remove D11 when using the v4 CPU board on a v4 chassis. When using a v3 chassis D11 needs to be present.