Bad battery issues can be either, bad battery plugs, one of battery's elements is dead, you should introduce load to each element and veridy it'll hold around 2V. There's a tool for that.
Also acid density should be measured, volts alone do not tell the whole story, unless you measure battery output volts under load(driving, lifting or those two combined).
Also worty to check contactor, emergency kill switch pins for even voltage.
Abouy turtle stuff, you shoulf check screen, battery led display for error /event messgas. If it shows 19xx you can be quite sure there's error in safety equipment.
I don't have a ton on jungheucirch experience but can tell you that no charging system or machine can operate without 24 volts...if they are separate batteries find the 4 that test at at least 5.2 at piece and run a series circuit to charger...see if charger kicks up voltage then...if doesn't after having descent batteries...issue with charger itself
On the one with contactor not closing verify 24 volts in and both positive and ground inputs sending in whatever is control voltage 12v or whatever...if all test good hit contactor gently when trying to activate...then hit drive motor gently one with work...that will tell you where the issue is
As for the forklift verify power when going forward at coil...then flip forward and reverse wires to see if drives