Originally Posted by catlinB
if your near any truck dealerships you should try pricing batteries there. the local parts places here wanted $100-150 per battery for 850CCA. i got two 1000CCA batteries from the local international dealership for $100 a piece. there a little taller, but didnt have any contact with anything. warranty was the same or better then some parts stores also. with higher CCA and less $$.
Can you check and share with us what Group # those batteries are? I'd be interested in finding a larger size that fits.
Originally Posted by TulsaDave
Yes they isolated my batteries. My wife's uncle runs an autozone and I trust him. After I fire it up sometimes it'll read high 11s for a little bit, then instantly shoot to 13+. I'm thinking the CTS is having an issue with this one.
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The delay in voltage rise is normal. The alternator is not energized until after the glow plugs turn off to reduce alternator stress.
Check voltages with a multimeter with both engine off and after it's started and alternator is charging. You are correct that it appears your alternator is fine, but if 11.5V is accurate, then you have a battery issue. I would guess one battery has a shorted cell, normally this takes battery voltage down to 10.5V or so, but with another good battery in parallel it could settle higher. Also, when you check the OFF voltage, disconnect the grounds so you can check the batteries individually.
Your batteries testing at over 13V tells me they didn't test them correctly. Unless the alternator is running or a charger is connected to a battery, it won't read over 12.7V or so. When they load test them, they normally drop into the 11V range.