Originally Posted by Mahakal
After following the suggestion given, I found the problem with the power converter. Changing converter will be the next project.
How did you determine the converter was bad?
On many chargers/converters, there must be sufficient voltage on the output (12v side) to engage a safety relay. Dead/very low batteries offer a very low resistance load on the converter so if your batteries read very low voltage, the converter will be shut down and not produce any output to prevent high current from the converter. High charge/discharge current could make the battery explode. Very dangerous,
I suspect the low load voltage is a most probable scenario in your circumstance, however by letting your batteries go dry you may have caused damage to the converter before the shutdown relay activated.
While your batteries are likely toast, but they may recover somewhat if you try a low current trickle charger overnight and see if you can get the voltage back up, (I suspect there could be internal battery damage but perhaps the converter shut down before too much damage occured.)
You could also connect you chassis battery to the output of your converter to test if my theory of the relay shutting down the converter output,
Many people have commented about "water" levels in batteries. The liquid in the battery is electrolyte. If the battery is charged, that solution is sulpheric acid, NOT water. Sulpheric acid is extremely damaging to the skin, can make you blind and will eat through many substances.
When a battery is charged, extremely flamable hydrogen gas is emitted from the vent holes in the cap. Be very careful no sparks, flame or any igniting item comes near that gas as the batteries charge,
Suggest you get a hydrometer and check the electrolyte specific gravity and record the levels.
Good luck, hope I was helpful