I understand that the ABYC standards say that you shouldn't depend on ONLY a soldered connection for as a MECHANICAL connector for battery cable. A properly made mechanical connection with a special crimper or hammer connection is probably adequate and is the usual method; however, soldering and using a crimper is probably okay.

Also, be careful with dyelectric grease -- it may actually cause problems. It's probably okay on the outside of the connection as a anticorrosion coating -- but keep the copper to copper connection as 'Clean' and direct.