When is it important to get a new alternator... like how big of an amp (generally) do you think warrants a new alt. I can't find the HOT rating on my stock mazda3. My friend just threw a deal at me on an Arc Audio 1500XXK, but I see it draws alot of power and is an A/B class amp - would I probably need a new alt even if I didn't push the amp - prolly just a 400-500watt load?