At this point, you have two choices,
1. Either remove the battery and take it to an Autozone, NAPA, O';Reilly's, et all and have them
load test it.
2. Buy the load tester yourself and check it. You can get a decent load tester for under $40 on sale. They are INVALUABLE for testing any 12 volt battery and also seeing the basic performance of the charging system. Since you seem to like Amazon, here is one for you.
Buy Schumacher BT-100 Battery Load Tester and Voltmeter - 100 Amp: Battery Testers - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
Short of load testing the battery, every thing else is a waste of your time...............Stop guessing what parts might be bad and actually test and diagnose the problem. Chances are, the battery is NOT supporting the load demand and that is your problem. But don't buy a new battery without
LOAD testing the battery you have. Any other test of the battery means nothing in this situation..............so don't even waste your time.
As Stan, Coaltrain said, these batteries cause all sorts of odd electrical issues when they are failing. Some fail slowly, others fail immediately. You can only know for sure with a battery load test.
2 year old battery with battery tender is as likely to be bad as is it is good. Only a load test will tell for sure.
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