RYOBI RM300e Electric Riding Mower --- acting like low battery...next steps to troubleshoot?

[StackAttack]

I have a Ryobi RM300e electric rider and when I got it out to mow this past weekend it acts like it has a low/bad battery. It will drive forward or backward for about 3 feet then kinda die off and beep 5 times. Acts like the battery is low although it was on charger and should be full. When I test the charging port with a multimeter I am getting 54v but the battery LED gauge (under the key port) is showing only about a 20% charge. I'm wondering next steps to test batteries further to ensure they are in fact good (maybe weak under load?) and/or diagnose further to see what the issue is....

Help?!

 

[StackAttack]

Also, if this gives any additional info -- when you plug it in to charge the light on the charging port of the mower begins to flash (like it's charging) but then after 30 secs or so goes solid as if it's out of the "fast charge" mode and charged and ready at 100%......when it's obviously not. Engaging the blades does the same thing as well -- they spin up for about 3 secs then stop and it beeps 5x...same thing acting like battery is low....

 

[cswain]

Did you find a solution?