I've been in four or five clubs and commercial operations that have used both. The electric carts seemed to have better speeds for towing gliders with a wing walker -- that is, they could tow at about the same speed as the ground crew. With gas I was on the throttle, back off, back on, etc., just to stay slow enough to avoid running away from the wing walker. Perhaps you could gear the cart down and avoid this.

I will admit that batteries are an expense and they have to be kept up. But at my last operation (commercial) the line crew were given the responsibility of tending to batteries on a regular basis and we got good results from the batteries -- two years or more operation on an almost daily basis, running out and back to the line (about half a mile each way) numerous times, and towing half a dozen or more gliders out and back. We had battery problems very rarely as long as the ground crew tended to water levels, corrosion prevention and charging on a regular basis.