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#81 (permalink) Old 02-26-2013, 12:22 PM
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Costco does not sell Optima near my place. Wonder if they sell anywhere in Canada at all.
Can you tell me how much you pay for the Optima yellow top?

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#82 (permalink) Old 02-26-2013, 01:37 PM
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the group 24 is about $200 here at discount auto stores. There is not a lot of price variation. I saw them at Costco awhile ago and I am going there anyway today for other stuff, so I will let you know their price.

It appears that the larger group 31 could fit with a little modification to the battery tray. I'm going to take a close look at that today before I buy the smaller one. There is a heat shield on the oem battery; I think especially with the V6 the battery gets too hot, and that shortens its life. If I put in the larger battery I need to see how much closer to the engine it has to be and see if I can devise an adequate shield.

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#83 (permalink) Old 02-26-2013, 02:53 PM
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Quote:
Originally Posted by bob-o View Post
The attached paper shows that a battery at resting voltage of 12V is only 25% charged. I got in the car yesterday and it was 11.7V which is about 10% charged. Lead acid chemistry has not changed.
Well, your battery must have some different something than any deep cell battery because all three types in their table Battery voltage and state of charge - Energy Matters show a 0% state of charge at 11.8V or lower.

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#84 (permalink) Old 02-26-2013, 03:14 PM
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Yeah, when it is down below 12v it is pretty much dead. The difference is usually what voltage different graphs call 0% capacity. Operating lead acid batteries down that low drastically shortens lifetime. Whether they are deep cycle or rapid cycle, the chemical reaction that determines the voltage at rest is the same. Differences in the charge discharge curves are due solely to the construction methods and battery size.

Deep cycle batteries use thicker plates to reduce the problem, so they last longer when they are discharged further down than the auto type batteries with thinner plates so that the increased surface area makes them faster to charge and produces higher current. The optima yellow top is a compromise design to produce high starting current and deep cycle performance at the same sort of cost as all season tires, it is not the best at either, but best compromise for someone wanting to use battery power when the car is not running. I'm headed to Costco...

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#85 (permalink) Old 02-26-2013, 04:08 PM
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Bob have you used a temperature sensitive hydrometer to test your battery, more accurate that voltage readings because voltage is only part of the system.. Current is also a part as is plate cleanliness, sulphates, and the electrolyte.

The electrolyte may be partially blocked with the sulphates and an equalization process may transfer back the complete electrolyte to a full conductor.

I find with my 2011 Sport I must equalize the battery 2x a year, add distilled water 2x a year in order to keep terminal voltage as high as possible with a reserve capacity in place.
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#86 (permalink) Old 02-26-2013, 08:24 PM
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The guy at Costco says they stopped selling Optima batteries about a year ago. I'm going to take a closer look at putting in a group 31 before I buy the 24.

The very best measurement I can make is to measure the battery capacity in Ah, and plot the discharge curve, and that is what I will do soon. I am not in too much of a hurry because I carry an extra booster battery in case the first one goes dead. I go out pretty far sometimes and there is no cell reception and no help if the battery goes dead so the extra weight is worth it.

I have a desulfator I built for EV batteries, and I will run that on the battery after I test it and see if there is any improvement. Sulfation does not affect the open circuit voltage significantly, only the output current and capacity.

Bear in mind this is a 3 month old battery, not 3 years.

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#87 (permalink) Old 02-27-2013, 02:28 PM
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Well, I charged the battery yesterday, it came off the charger and measured 12.6. After sitting in the car overnight, this morning it reads 12.0. I checked the current drain and it is <0.1A. Before setting up to measure the capacity I turned on the high beams for less than a minute, the voltage dropped to 11.5V and when I turned the lights back off the resting voltage was back to 12.0.

I don't see any point in measuring the capacity, clearly the battery is junk. I can't find my hydrometer, so I'll get a new E-Z Red next time I go to town for <$10.

The dealer put his tester on the battery and it reported 720 CCA. This test is supposed to be done at 12.0V for 30 seconds. How could it possibly have done that when it drops to 11.5 for just the headlight load? It is supposed to have 125 minutes of reserve capacity at 20A and it is half dead after a minute at less current. I will take the battery to the dealer and insist on a replacement, then put the replacement in my tractor. If it doesn't start it's never far from home.

If they continue to claim the battery is fine they will hear more about it from Toyota.

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#88 (permalink) Old 02-27-2013, 05:23 PM
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Quote:
Originally Posted by bob-o View Post
The dealer put his tester on the battery and it reported 720 CCA. This test is supposed to be done at 12.0V for 30 seconds. How could it possibly have done that when it drops to 11.5 for just the headlight load? It is supposed to have 125 minutes of reserve capacity at 20A and it is half dead after a minute at less current.
That's a very good question . One answer is that the CCA rating is defined as the current a lead-acid battery at 0° can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).

This test indicated your battery provided 6AH (720A * .008H) during the test, but it's not really a measure of battery capacity, but rather a measurement of internal resistance amongst other things. The battery was not depleted during the test.

On the other hand you say that your battery is rated at 20A for 125 mins, which indicates it's capacity to be 41.7AH.

So your argument that your battery is suffering from reduced capacity was not proven incorrect by the CCA test.

After this thread has gone on for so long aren't you curious to find out what the real capacity of the battery is. I for one am really interested in how your resting voltage theory compares with a real capacity measurement. You could also try De-sulphating the battery to see if it changes anything.

Of course to do the test properly you may have to bring the battery indoors to run the test at the standard temp of 80°.

FYI the official definition of RCM (reserve capacity minutes) is the time it takes for the battery to reach 10.5V with a 25A load at 80°F. On my battery the RCM is 120 mins resulting in a 50AH battery.

EDIT: Battery capacity tests are normally performed with a load of C/10 or C/20, not 25A. This site says that battery capacity in AH is roughly eaqual to the RCM in minutes divided by 2 , or C(AH)= RCM(mins)/2. So my battery would have a capacity of 60AH

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#89 (permalink) Old 02-27-2013, 06:09 PM
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I dug around out in the barn and found my EZ-Red so I checked the battery specific gravity. The cells measure all over the place from 1.225 to 1.250 so the battery is not charging properly even though it was run at 14v overnight and the current dropped to a half amp or so. For this kind of imbalance to occur in a new battery so quickly seems unusual.

I measured the battery impedance at 1 kHz with my HP milliohmeter to be .0035 ohms. To get 420 CCA the voltage would drop .0035 * 420 or about 1.5V. This makes the Toyota CCA number believable. When they measured the battery voltage the car had just been shut off and it was 12.57. If they had turned the headlights on for a minute or two it would have dropped to 12.0. I don't know if that would have failed their test.

I will run the desulfator on it overnight and retest the gravity tomorrow. If I can get it up to 1.260 in all cells I will test the capacity then. I will still not depend on it.

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#90 (permalink) Old 02-27-2013, 06:58 PM
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I think you are over thinking the battery condition. Does it still start and run well?

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