Yes, without testing and measuring to let numbers tell you exactly what's wrong and how to fix it, you'll be randomly replacing perfectly-working parts with brand-new perfectly-working parts and nothing changes. End up wasting LOTS of time and money when you can find problem in less than 5-min with multimeter. You may have problem with charging system, or wiring-short in harness that's draining battery. Replacing battery will have last just enough for couple rides before it too is dead like current one. Simple test for battery:If you replace the battery that will probably replace some problems, though I would favor load testing it first (unless you know its age - at 4 years, I tend to replace mine because lead acid batteries usually live a 4 to 5 year life). Just replacing parts w/o diagnosing a problem is an expensive way to troubleshoot.
1. measure battery-voltage with everything OFF, volts = ???
2. measure battery-voltage with key ON, kill=RUN, volts = ???
3. measure battery-voltage while pressing start-button, volts = ???
These numbers will at least tell you right away if battery's good or needs charging or is outright bad. No need to waste time & money replacing if it's good.