A crimp has the best electrical connection, if you're concerned about corrosion put a piece of heat-shrink with inernal sealer, available at most electrical supply and automotive parts places. An auto-electric, industrial industrial supplier, or marina will be able to crimp for you.

Solder connections are higher resistance, and can come loose over time. Even if you prefer solder, crimp first and solder to seal it.

If your alternator is bad, I'm not sure why you feel a need to upgrade. If you have additional loads I understand the need, if only stock loads the factory alternator with a proper size battery is good. If it's not charging properly, ... you've found the problem. Quite possibly just the regulator, which on your alternator is a 10minute job and last time I needed one it was under $40. I'd start there unless you have the ability to test the output.

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Gone to the dark side

- Jeff