Car starts fine when cold, but once the car is warm it acts like the battery is low when starting, sometimes it stops turning the motor over completely...very odd. Battery is brand new red top. Voltage drops to ~10vdc when starting. It's also relocated to the trunk.

 

How many cold cranking amps is the battery rated? What you have may be too small. Fitted in race cars to save weight is a common reason for the Optimas. For a S2000 capable battery any voltage drop below about 11.5vDC indicates a weak battery. I've never been impressed with Optima batteries for the same reasons you're listing.

-- Chuck

 

Trying to figure out the same issue. After my car gets fully hot, it needs to cool down for about 10 minutes before it will start again. My battery also tested good, at temperature and under load by the dealership.

 

Resistance in a metal rises fast, as its temperature rises. IIRC, copper rises 10X, as temp goes from 0ºC to 100ºC. Rise in resistance lowers current flow. Prolly, just enough to keep this battery from turning the starter, in your car.

 

Voltage drop test is a good starting point. Starter amp draw should also be done as well as checking charging system.

 

700CCA. This battery is not small. From what I looked up, it seems like a drop to 9-10vdc while cranking is normal. I had to go with a sealed battery as it's in my trunk and im not venting.

 

Did you measure 10V at the battery or engine bay?

 

It's sometimes a sign the starter is going, but not always. Battery is new so it's either the starter/starter solenoid or the ignition relay or starter cable.

 

First mention the battery is not where it belongs! Insufficient cable size to the starter is the first suspect. Easiest way is to just double up the cables. And check the ground (or maybe start there). What size cable are you running. Anyone know how many amps the starter pulls?

-- Chuck

 

All my measurements were taken live from AEMdata through my infinity. I have a 2 gauge ground and another 4 gauge ground going to another location. Grounding is def. not a problem. Using a 4 gauge for power. The fact that it starts just fine when cold throws me off. My fusebox is tucked in the fender so none of that is getting heat soaked, nor is any of the wiring. The only thing exposed would be the power cable for the starter...and its the stock cable.