Odd no-start problem.
 

My kid’s boyfriend’s car was having a problem. (05 element, auto tranny, 2wd). It was a very weak start sound, like a dying battery. Any time I’ve ever heard this same slow start sound it’s always been the battery, dozens of times. So, I just replaced the battery. Same slow turning over sound with no starting.

Heard the starters were notorious, car has like 130k on it, so I went ahead and replaced it. Slow start sound then nothing at all. I can hear the fuel pump buzz by the way.

Went ahead and and swapped out the plugs, the rubber on the boots tore so I put in new coil packs too. Still no good.

Swapped starter relay, no good.

Replaced ignition, no good.

What at am I missing?

Would have loosened serpentine belt and tried to see if it would crank any better
Reason is one of the accessory pulley can be seized. ie., alternator, AC compressor, idler, etc.
Also, clean up connections and chassis ground along with engine ground strap.

Belt
 

Will try the belt idea, good thought. I cleaned the ground going to the body, will look for more.

Well another reason for slow crank could be clogged exhaust.
The test would be to remove the upstream O2 sensor and see if it starts and runs.

Well, I did replace that sensor a month ago, will try that too

The only thing else I can think of is corrosion on the battery to starter cable
Ohm testing would show there is continuity
However, a loaded circuit might show it has high resistance
Sometimes don't need a new cable
Just clean up the terminal or cable ends

Hope you figure it out.
I've got nothing else

Tried to take tension off belt but apparently you need a specific tool for the tensioner?

will double check the cable ends soon.