Hi, i have bought a second hand oset 16 36v spider for my daughter for Christmas. Taken her out on it and it seems really slow. On full throttle with the speed adjuster all the way up it goes walking pace. The guy I bought it from said the batteries were about 1.5 years old and it had been stood for about a year. They are lucas 12v 10ah batteries, i have tested the voltage in each battery after being fully charged and are showing to be 12.7v each. Tested the voltage just before motor on full throttle and its showing 37v.

I've also taken the motor apart and tested for any signs of damage to the bearings and brushes. All seems fine. Could it be that they need new batteries or could it be something else?  Thanks. 

I would definitely say batteries went bad, we had 3 of those little electrics one 12.5 and 2 16's, they should go faster than running speed, faster than me anyways. You would have to test the voltage under a full load to get an accurate idea. We went through more than a few sets of batteries, the best bang for the buck I found was on Amazon.