is 1-year old 6v Optima going bad?

[Dave Wildrick]

I just returned to Houston from the Hill Country Rallye held in Kerrville, TX, in my 64 C coupe. The generator was rebuilt by Zim's a couple years ago. My 6v Optima battery is exactly one year old. I had no trouble driving 265 miles from Houston to Kerrville. We drove all day long for hundreds of miles/day for 2 days straight. No issues except that the car was getting increasingly hard to start toward the end of the 2 days. On the return trip to Houston, we stopped for gas in Seguin, TX, about 100 miles East of Kerrville. After the fillup, the car would not start. So, I got a jump start from another guy at the gas station. I kept the motor running for over 100 miles from this point all the way to I-10 and Sam Houston Tollway 8. When I exited I-10 about a mile further East, the car died when I got to the traffic light at I-10 and Gessner St. A couple big guys helped me push the car out of harm's way, and a friend came and gave me a jump. I made it the remaining half mile to my girlfriend's house, with the motor popping and snorting. Checked the battery with a voltmeter and it was at about 4 volts. So, I conclude I was running on battery for most of the weekend. I put the battery on an AGM battery charger (not on boost) at about 10 amps I guess, for an hour and a half, and got 6V at 30% charged. I started the car and checked output at the battery and got 6.05V. Checked generator output at D+ on the generator to ground and got as high as 7.4V when revving the motor a little bit.
So I guess the generator is OK, but I'm not so sure about the battery. Not sure why it discharged so drastically over the weekend.
What's the best way to test a 6v Optima? What's my next move?
Thanks,
Dave

[David Jones]

Two things I would suggest Dave, do a load test on the battery, your local parts store should have a tester. No need to disconnect the battery to test it. Done in situ. Next buy a digital voltmeter that plugs into the cigarette lighter socket and monitor charging voltage in real time.

[Mike Wilson]

Also check the voltage regulator to make sure it is functioning correctly.

Mike

[Jim Liberty]

Guys, the same thing happened to my 2 year old 6V Optima this week. It is in my Crosley Pickup shop truck. I have been using Optima for years and this is the first complete failure. It would not take a charge. I've checked for a minor drain and nothing. I just put a new one in the truck. I'll keep you posted. .............Jim.

[Martin Benade]

If the car quit while running it sounds more like the generator isn’t performing. It should supply enough juice to run the engine, unless the battery is internally shorted. When you jumped it and drove the last short leg it was popping because all it had to run on was the tiny charge you got into the battery by jumping it. The battery may well be just fine (not that I like Optima’s)

[Jules Dielen]

Load test is the way after the battery is fully charged. If that checks ok, check what your regulator output is. Your generator warning light works?
Either way, optimas are definitely not what they used to be.

[Harlan Halsey]

Cars run on the generator, not the battery. The battery only supplies about 150 amps for a few seconds while running the starter motor. The voltage regulator maintains the system voltage to 7.2 volts when the generator RPMs are high enough to put the red light out, about 1500 RPMs. The generator maintains voltage because the regulator varies the field current to make it so. The system can fail if the generator becomes inacpable of putting out enough current or if the regulator fails to properly maintain the field current.
When the system fails, the voltage falls to the battery voltage, a little above 6v. A fully charged 80 ampere hour capacity battery can support the 3-ampere ignition drain for a long time. The greater the drain, the shorter the battery life.
In this case, the failure is likely either generator or regulator, not the battery. I'll venture a guess that the generator brushes are shot.

[Greg Bryan]

Before you toss the Optima, try to recover it with this method:
Find a fully charged 6v battery
Hook it in parallel to the Optima + to + and - to - with jumper cables
Charge both batteries as they’re hooked up in the manner described above for 12 hours
This process will recover a depleted absorbed glass mat (AGM) battery
Charging a depleted AGM with a regular battery charger usually won’t work unless you use this process
Regarding your generator, if you ground the field, a 6v generator will put out up to 18-20 volts at 3000 rpm - only do this momentarily and have the generator harness not attached to the generator
You can look up several charging system tests in the Registry magazine on the 356 Registry site Volume 40, Number 2 - July/August 2016

[George Hussey]

I have had recent problems with the red top optima battery in my Ford GT. The first factory one lasted from 2006 to 2019, the second one 2019 to 2020 and not the third good so far. I had heard that when they transferred production to Mexico the batteries went down hill

[Wes Bender]

There have been instances where the Optima batteries have failed early, but it isn't the norm. As Harlan states, the car uses the battery primarily for starting and is powered by the generator (controlled by the regulator). I would use Greg's method of charging your battery and then take it to your local automotive parts house and have it load checked as David recommends. If it fails the load test, replace it with whatever you trust. If it passes, then the problem lies in the generator, regulator or wiring. These are pretty simple systems.

[Martin Benade]

So quitting while driving tends not to be due to the battery. (Post #5)

[Mike Wilson]

I guess I have been lucky. I think my first 6V Optima lasted almost ten years. I'm on my second and it's at least 6 years old. As far as driving on the battery alone, shortly after I bought my car, I attended the 356 Concours at Dana Point but in the way home, the red generator light came on. The engine wasn't overheating so I knew it wasn't the fan belt so I ignored it as I was fairly closest home. Turns out the small silver voltage regulator had failed and fried the generator. So, the 8V (long replaced) battery wasn't being recharged and I made it home on battery power. Aside from providing spark, there wasn't much of an electrical demand, just brakes and turn signals.

Mike

[Paul Lima]

As people have mentioned, there are three components you must analyze: Battery, Voltage Regulator, and Generator. The process is MUCH easier if you have a voltmeter. (1) with the engine off, the battery voltage should be in the range of 6 volts. Right after driving, this number should be more like 6.5 volts. After a few days, maybe 5.8 volts. (2) with the engine running above 2500 RPM, the battery voltage should read about 7.4 volts. If it is significantly less then the battery is not getting charged. This could be due to a bad generator or bad voltage regulator. Unlikely, but possible, a shorted battery cell could drag a perfectly running gen-vr combo below the 7.4 v. If you can put a charger on the battery overnight and see a terminal voltage of 7.4 on the charger, and 6.5 or so when you turn the charger off, then check the voltage with the engine running again. If you get normal voltages but continue to have a problem then it is almost certainly the battery. Greg Bryan's comments above may be a way to resurrect a dead Optima, but my experience with recent Optimas would suggest buying another brand (my preference is Odyssey)

[Dave Wildrick]

Load test is the way after the battery is fully charged. If that checks ok, check what your regulator output is. Your generator warning light works?
Either way, optimas are definitely not what they used to be.

My generator warning light is red before I start the motor but goes out while it's running. The light never came on while I drove all those miles--until the motor quit.

[Dave Wildrick]

In this case, the failure is likely either generator or regulator, not the battery. I'll venture a guess that the generator brushes are shot.

Zim's rebuilt the generator no more than 1,000 miles ago. So very unlikely that the brushes are shot.