The OEM batteries in our truck are just past 5 years old and likely are nearing end of life. Should I bother testing them or just replace? If you think I should test them, please recommend a good automotive battery tester.
Carbon pile tester is the gold standard, but these work decently enough and highly rated by users and the Project Farm guy, if you want to search for his review on testers from a while back on YouTube. Ancel BA 101.
I have the Ancel, which was cheap (<$20 at the time), and does provide some data.
But keeping in mind its limits as a conductance tester, the conclusions it provides are no better than the simple household battery testers with the green/yellow/red scales to indicate the health of a cell based on its sole measurement of unloaded voltage.
I bought the ANCEL a couple of months ago on BITOG recommendations. The numbers it generated were very close to what the Batteries Plus tester and a parts store tester showed. Be aware it's very sensitive to a good solid contact of the clip on the battery terminal.