Voltage question

[Yoni_d]

Hi Guys

Sometimes I feel that my battery is not good enough since the engine cranking sounds weak and despite that it is cranking, it doesnt always starts.
I have decided to check if my electrical system is ok.

Here are my findings:

Engine not working:
Alternator: 12.33V
Battery: 12.35V
Main + terminal (in the engine compartment): 12.33

Engine idling:
Alternator: 13.65V
Battery: 13.44V
Main + terminal (in the engine compartment): 13.39V

2500 RPM:
Alternator: 13.65V
Battery: 13.45V
Main + terminal (in the engine compartment): 13.42V

Can you please tell me if it is normal? should I make any other tests?
What can be the reason that the engine will not start even if it is cranking? I have noticed that if it is cranking and doesnt start when I attach another 12V battery it starts right away

Thanks for your help!

[Fredfox]

Do a load test on the battery, your readings look good.
Either a bad ground, bad battery or bad starter.

[MPDano]

Dang, I wish I had such good readings.

[Maleficio]

Fred's right. Scrub your grounds, but replace the ground strap on the passenger side of the engine, bottom side, attaches to the body. It is unsheathed from the factory, and is probably highly corroded. Replacement ground cables can be bought at any parts store for less than $10.

[Yoni_d]

Thanks but if the readings are good, why should I check the grounds? I mean, the starter does rotate the engine - but the engine sometimes just dont start without an additional battery :\

I think I will do that load test on the battery since maybe during the starter the voltage drops and then the electrical system doesnt get its 12V...at least the readings are good