You need fine strand with as many wires as possible for DC voltage. That 4-6-8 strand is for a/c and does not carry D/C like you need. One of the best is quality stereo power cable in the size you need. Not really cheap but will give you the best performance. The clear coating if exposed to a lot of sun will turn black on you is only draw back. You could also get marine grade tinned wire which again isn’t that cheap but for the length not a bank breaker and worth it in the long run.if you google it you will find some places that will cut it to length and install connectors of your choice on ends.