The charger lights will still turn on even if the charger is bad. The charger should start up no matter what. It should be yellow and blink green for at least 10 seconds before both lights turn solid. If both light start solid there could be an issue with the charger.

If one of the break switches is bad, hydraulic functions will still work and no wrench light or codes will appear. You might see sro, that either means the tiller isn't in netural during start up or one of the brake switches is giving a bad input.

Still my best advice is to measure the overall battery voltage idle then put a load on the battery by using hydraulics and driving to see how far the battery voltage drops. If it drops more than 20% then one or more of the batteries are dead.