Has anyone checked the battery voltage at the jump terminal while cranking their car to start.

I ask because yesterday, hot outside, stopped at hardware store, car wouldn't crank, nothing, no clicks, dead.

Gauge in car who's 12.5V or so, tried to crank, drops to 10.5 on gauge, not very accurate but drops way down and no starter action, clicking or anything.

So called AAA, thinking the rebuilt starter was dead again, to get tow home.

AAA shows up, still no crank, says lets try jumping, vrooom, fires right up. Get home, shut car off, starts up but voltage gauge shows pretty low during cranking, right up below 14v when running. Alternator is working fine.

So, 1 year old battery NG, it was a Deka second, their factory store is nearby, maybe it wasn't worth trying it. Heck with it, SITM is coming up and I an't going to miss it, off to Sears who has battery new battery in stock. Install it, fires right up.

I decided to check voltage at jump post, not running, shows 12.6v, cranking, drops to about 10.8V, seems to turn over faster, started right up, reading 13.7v running.

I'm thinking with the heat, the other battery internal resistance increased enough, not putting out enough juice? All grounds and connections are clean and tight.

Is 10.8v -10.9v while cranking normal?

 

Usually battery function decreases as the temperature drops, not rises. Unless there is something wrong with the chargign system. Did your battery get boilled, over charged?

 

No, it seemed fine. Charging system is working fine too.

 

Ground strap at the battery may have internal corrosion.

 

Does anyone know what the impedance threshold is on that strap before functional failure happens?

 

Ground strap, good suggestion, but it is new as is the cable from battery to starter. I may check to see what the voltage drop is cross that when cranking.

 

Locate all voltage drops and address the largest ones first.

Get a helper. Not necessary if you have a DVM with MIN/MAX/AVG function.

Make a long (15 ft. ?) meter test lead.

Disable ignition.

Measure directly across battery while cranking.

Move the positive lead “one connection” away from battery while keeping the negative lead on the post and crank again.

Continue one connection at a time until you are at your destination.

Repeat with positive at battery and moving negative one connection at a time.
This includes positive at battery and negative at starter itself.

 

10V while cranking would be fine. If it's cranking.

Ignore specific readings on that 20yo dash gauge. If it's more when engine is running than when off you know the alternator is working. That's about all you can expect.

If you suspect the battery, pull it and take it in for a free test at your friendly local auto parts store.

Also, search for hot-start failures related to a weak wire to the solenoid. I haven't suffered that so don't know much about is except that it exists.