(Pack of 5) 20W 10R 10 Ohm 5% Power Wirewound Ceramic Horizontal Cement Resistor

Little overkill but it will work, some people over complicate stuff. Here is my setup similar to yours, nothing complicated, straight forward. https://www.reddit.com/r/SolarDIY/s/dXXWe1sXCq Use cheap resistor like these. https://a.co/d/0iNgkpt1 Hook to negative cable and tap negative battery terminal, this would control the spark, you can do it without the resistor but there will be a spark, which could be little or a lot. Hold for about 10 seconds, then remove resistor and hook up negative terminal to negative battery.