I have 2x 40AH batteries in my gopher. Std is 34AH wet cell. I discharge them at abt the 3hr -3.5hr rate for up to 2.5hrs. The batts are 4mths old, and I'm noticing acute random speed variations with no change in Vcc after abt 30min running as of last 2 weeks. Batts test ok, and motor has new brushes. I can't verify connections as I can't bend/kneel down to it. Weather is warmer now. What difference will it make if I interrupt discharge for 5 min every 15min? How much power is being taken from the batteries at present rate and ditto if the rested rate? What lifespan can I reasonably expect if used at least 3x/wk? I use a 10A 4 stage intelligent charger, and usually float the batteries unless using them. Temp is abt 30degC atm, and on its way to 40+ in shade. NB a Daning bicycle computer appears to have fried in direct sunlight--recommend me something better. I need the long range to get anything done, shops etc are just too far [~1hr] for anything less, tho' I could reduce speed..... Avg. motor current varies from abt 6A to 30A load dependent. most local hills are modest and short, taking only 1 or 2km/h off the pace, but sufficient to increase Avg current to 30A for 1~2min at full speed.

 

So the problem you're trying to solve is the speed variation? There are a lot of possibilities, but a loose connection at the batteries is probably the easiest to check for, assuming someone can help you. Is there anyone who can help you by checking all the connections related to the batteries? Being loose, having corrosion, etc..