Odd issue.. could use input

[Mgicm]

So couldnt find the exact forum to post but think it is more of a general issue. GMC 1973 truck... I went out this am, started without issue and drove 14 miles to our city. Shut truck off and came out about 10 mins later. Would not crank. Dash lights ok. I thought for some reason it was a hot start issue where the starter needed time to cool down. Why? A few other times this happened, we let it sit for 1-2 hours and it cranked right up. Today..three hours and nothing changed.

So finally had someone come out with a meter and jumper cables. Battery (2 months old) showed 12.5 volts. I gather not enough to start this chevy 350? Jumped it off friends car and she started like nothing ever was wrong.

Drove home 14 highway miles...still showed 12.5v. Would that immediately say alternator problem? Nothing was on such as headlights, radio, etc. Nothing. Alternator was just replaced 2 months ago. Or does this possibly relate to a battery issue like not holding a full charge...or something draining it ? I can check voltage tomorrow am.

Sorry for basic questions..

thanks GP

[bilfman]

Battery is shot. It the amps you need to crank. Volts can be 12 and the battery can be shot. I bet if you did a load test on the battery it would fail. I am sure if you replaced it things would be fine.

[Mgicm]

Ok will rip out the battery tomorrow and bring to store for load test.

[Dead Parrot]

If you have a volt meter, check the battery while engine is running. Should be around 14~15 volts. If you have the 14 volts, suspect battery. If still around 12, suspect alternator. Double check both battery cables and alternator connections. Old cables can look good on the outside and be bad on the inside due to corrosion.

Don't overlook the possibility of starter brushes reaching end of life.

[Mgicm]

I'm going to add a whole extra layer which I should have mentioned.

I have a dual Battery setup with a battery isolator. The second battery has a inverter connected to it for items we run in thee truck. When checking batteries, the second showed 12.8 volts. The odd thing was when it would not start, I could not get the inverter to turn on at all. Once we jumped it , inverter turned right on. Odd. To further muddy the waters, I have a backup camera on a switch which is plugged into the fuse panel accessory terminal (main battery ). When it would not start, the camera would not work. After we got it running, everything worked well. With 12.5 volts, I would think an accessory item should work well regardless no? Headlights worked fine when it would not start as did horn. Didn't try wipers.

I am going to disconnect the isolator and second battery to concentrate on a single battery.
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