Hi all, Have been busy completing the build on the remote mower with all sorts of combinations of electrickery. Managed to get a 24 volt alternator hooked it up with batteries in series and ended up having the same symptoms as before.The final verdict is that I need more Hp as per my original question. The 24 volt system made the motors run too fast and made the mower travel speed difficult to tame. So I went back to the 12 v setup. The Sabertooth motor controller decided to pack it in (it was purchased second hand) and another week went by without mowing.I ended up buying a 2 x 32 Amp Sabertooth motor driver to give me a bit of spare capacity I used this time to paint the mower and tidied everything up. The link below shows the finished product (for the time being).
Many thanks to everyone's comments in trying to sort this out