Grove RT60S no longer drives.

I have a Grove RT60S crane.

Everything used to work and it drove around.

At some point I noticed that sometimes I have to put it in and out of Drive gear to make it go. But it was all OK.

Now it sat for like 3-4 months, I started it occasionally and the batteries were charged. However, it no longer wants to drive. If I put it in drive gear, it shakes a bit, wanting to go, moves maybe 2 inches and no further. It is as if it lost all its driving strength.

Any idea why this might be...

Grove RT60S no longer drives.

Grove RT60S no longer drives.