The power of my Sullivan Dynatron starter has deteriorated and using double batteries caused the trigger to weld together. (despite it being rated unto 24V. A search on the internet revealed this is common problem which is very disappointing when they currently retail ITRO £115.
My solution is to switch the current with a 70A automotive relay. Ive added extra standoffs to the rear cover.
Ive added an extra high tech moulded cap (from an aerosol spray can). Then tin bashed some spare stainless to make a Li-po battery tray - more high tech (well a couple of bending machine (two bars and big mallet)
Finally, in order to use any range of Lipo from 3s to 6s, I needed to maintain a 12v supply for the relay. I modified a JST balance lead to tap the third cell and provide a nominal 12v supply with respect to battery negative.