DC VOLTAGE experts...

[ERA Chas]

This is not a ‘favorite battery’ or ‘Optima vs The World’ thread. It’s actually a request for generalized info about battery characteristics-not which is the ‘best’ battery so no pissing contests please.

The 2 year old Interstate in my street car (which had been perfect up to now) had begun to show 11.9 to 12.1 of late. I have been getting a ‘battery’ icon dash light which would come on at start up and glow 10 or 20 seconds. Sort of like an old time ‘generator light’. No CEL’s or codes showing. Headlights always bright and heaviest draws no problem.

The car is garage kept with 60K miles. It’s mid 40’s in the garage with ambients in the mid 20’s outside. At idle, it’s 14.6-14.7. So I’m thinking the charging system is fine and the battery has a bad cell or some other deficiency that won’t allow it to hold 12.6 or so which I believe is what’s normal for the conditions. I do not have a load tester or any other diagnostic equipment.

The 1 year old Optima in my Cobra will hold 12.5-12.6 without the Battery Tender. I use that during the cold weather. The Interstate is the premium which has a 30 month free replacement, 7 year pro-rated. It’s 80 amp, 640cca, 800 ca and 100RC. So I pulled it and got a free replacement. I know that if the car were outside on a 20’s day or snow storm, it wouldn’t start.

The new battery was 12.1 with a manufacturing date of August. I put my 10 amp charger on it for 20 minutes and it got to 12.7. At idle it was 14.7. Finished install and went for ½ hour drive. After that it was 12.3 and 14.6 at idle and I expected higher. I’m feeling that there may be a drain in the system. Forgot to mention upon disconnection to remove, I used a ‘settings saver’ which uses a 9 volt. Testing a new battery, it was 9.4. Total time disconnected was 3 ½ hours and when I removed the 9 volt it was 8.0.

So-what if any test procedures other than laboriously pulling a fuse at a time and seeing if the drain (if there is one) stops? Assuming that finds a draining circuit, then a wire/switch/relay test of that circuit? That is beyond my skill, equipment and brainpower. OR-is the battery fine at low 12’s in 40 degree and colder weather? If so, why the dash light? Again-didn’t have the problem for 5 years on the original battery and 2 years on the second until now. Any experienced answers appreciated.