Hi all! New truck owner here, picked up a decent running 2003 Mazda B2300 (which from what I understand is exactly the same as a Ranger?) for cheap and have been enjoying it. Have run into my first real problem and not sure what to try next.

I only drive the truck once every couple of weeks when I have an errand that requires it, daily driver is an old M3 that I've been wrenching on for 7 years. I've been doing my own mechanical work for a long time, but the M3 is really the only car I've ever worked on and know.

Anyway, went to drive the truck a few weeks ago, and it wasn't starting. Figured the battery was drained from sitting too long, took the battery out and charged it up on my CTEK MXS 5.0 charger. Put it back in the truck, it fired right up.

Don't drive the truck for another few days, go to turn it on, and won't start again. The accessories have power, and the starter is turning over, but no start. I figure the battery's probably pretty old and dead at this point, there was a lot of corrosion on the terminals. I clear up all the corrosion on the leads, and go get a new battery from autozone. Put the new battery in but get same behaviour: accessories have power, starter turns over, but no start.

So, what seemed to be the battery going out actually isn't the issue. Not sure what else to check? Any suggestions on what to check next or what common causes for this are? Even though it's not the battery it seems electrical related because the first time a battery recharge fixed it.. maybe alternator? Gas gauge is showing just below half-tank. This is a totally new platform for me so any advice would be appreciated :)