So, I know the preferred way to lengthen a cable is to replace the entire cable, but...

I have a 4 ga cable running from the 30amp charger to a house battery.  I have recently paralleled my house batteries, and want to take this cable and add it to my starter battery, since I have another cable charging my second house battery.

I have purchased the Ancor heavy duty tinned copper butt splice connectors.  I need to add a 4 feet of the 4 ga cable to get it to reach the starting battery.  What is the best way to splice these cables together?  Should I press both cables in the butt connector, let the strands interlace some, then crimp, solder, and then heat shrink?

Thanks for the advise.