HI, I've got 36volt 2001 Shuttle 2+2 The cart was behaving as follows:

Showed Fully charge as per the battery meter.
I was driving along and the cart just quits, no light on the battery meter at the time of quitting.
I came back a short time later and the cart moved but, in a herky jerky manor but eventually smoothed out.
I thought, maybe it's low on charge, plugged in charger, charger did not kick on. I assume because the cart was fully charged (maybe a symptom?)
Now the cart just does a herky jerky motion and will not go far. Any ideas? Thanks

I do have 4 old batteries, 2011, with 2 new batteries, 2016. A friend of mine says I may need to replace the old batteries. Even though when load tested they test fine.