Optima vs. OEM 28800-21171

Interesting, maybe they've upgraded the specs ob the Yuasa part.

In any case I'll bet the "useable" amp hours is more on a 38AH deep cycled battery compared with a regular 46 AH battery.

 

I have been an Optima fanboi here for years, but I hope I have never claimed it was a stronger battery. I hope my claim has always been that it resisted going flat after a deep discharge or two.

We see the OEM battery fail after someone leaves a light on overnight. Not because we needed a single massive power draw it could not do.

 

I have also been investigating the AMP/HR capacity of the Prius 12v battery and came to a similar conclusion as yourself. Jimbo and I have a fundamental disagreement About my solution, but that aside I intend using a 55AMP/HR sealed gel AGM battery that is the same size as the OEM "I'll leave you to work out the numbers" but the chances of discharge are obviously even less and it is a deep cycle battery.
Having taken a close look at the battery I intend using, it could easily bee modified (drilling one small hole) into a vented battery I agree not ideal but very doable, but again I believe not required.

 

I think you're barking up the wrong tree here. The difference in Ah is pretty irrelevant compared to cycle life. Any battery that will fit in there is going to have pretty meager total capacity, and an improvement of 10-20% will make very little difference. Here's a quick example:

Lets say the car gets left on in ACC mode and is drawing 200W for headlights etc. That's roughly 16A. To the first order a 38Ah battery will reach 100% depletion in less than 2.5 hours. A 46Ah battery will still be 100% depleted in less than 3 hours. At best you gained about a half hour. In most situations that's not going to make any difference in ending up with a flat battery.

The real advantage in going with the optima should be cycle life. In battery design there is a direct trade between the amount of storage capacity and available amps in a given weight/size, and cycle life. For a given weight/size a "starter" battery will most always have more capacity and more instantaneous amps available than a "deep cycle" battery for this reason. This is important in a normal vehicle with a high start load demand, but much less so in a Prius. While is purely anecdotal, the experience of EV builders from the lead acid days illustrates this point well. It was not uncommon for EV racers to go with an optima red top battery to get the most possible power and range out of a given weight and size. The down side was the pack would only last 10-20 cycles, and that's not even necessarily at 100% discharge. For daily use, a yellow top would give less raw power and range, but would last 100s or even thousands of cycles at a typical 50-80% discharge and tolerate 100% discharge well.

I can't seem to find it in english at the moment, but here's an example of a yellow top cycle life chart that matches pretty well what I remember, showing 350 cycles at 100% discharge, and 1000 at 50%.

[

This is where the real difference should lie in using the Optima YT in the Prius. Lets say a typical Prius 12V battery should last 3 yrs under ideal conditions. Lets also say it has a 100% discharge cycle life of <10. The problem is these two factors are not independent. Every time you completely discharge the battery you are "using up" some of its life. Leaving your lights on a few times very quickly gets you down to a life of 1-2 years. This effect is also likely non-linear in reality. The older/weaker a battery gets the more of its "life" get used up in another discharge event. This will be less severe for less than 100% discharge, but even at 50% it will be taking significant time off the battery's life. Now compare that to the Optima YT. Lets say it has the same expected 3 year life (though likely its longer), but a 100% discharge cycle life of 350, and a 50% discharge life cycle of 1000. For a similar number of discharge events the effect on the optima's life will be relatively negligible resulting in a greatly improved effective real world life span.

I realize there are a lot of estimates and simplifications in there, but I do think this explanation matches up pretty well with peoples real world experience with OEM vs. the Optima YT battery.

Rob

 

I have no hard facts to back this up but most people seem to end up with a flat battery because they left on the dome or trunk light. Some because they left the car for an extended period of time. With a larger AMP/HR battery if a small light is left on overnight it stands more chance of handling the load, and is not going to be as deep a discharge, and if the vehicle is left for a period of time again it has more reserves to draw on.

 

Double post deleted

 

Miscrms I think there is a misprint on your graph the vertical axis shows life in HRS surely this should read cycles.
One other complication that arises is that batteries are usually given an AMP/HR capacity at a 20HR rate (1AMP for 20HRS =20AMP/HR - 5AMP for 20HRS =100AMP/HR) but when discharging batteries at lower rates the AMP/HR capacity increases. So if you discharge the 100AMP/HR battery at the same rate as the 20AMP/HR "ie 1AMP" its capacity can easily be 110AMP/HR.
If you discharged the 20AMP/HR at 5AMPs you would be lucky to get 3HRS use out of it.
Another point is that the only time we truly cycle the battery in the Prius is when we leave something turned on. I honestly state in the 4 years of ownership I have never done this and I have never bean in a situation where the car would not start, and I am still on the OEM battery. At 4years of use however I feel it prudent since I live in the back of beyond to replace my battery soon.
The Prius OEM battery in the UK is £90 (45AMP/HR) I can bye an AGM deep cycle 55AMP/HR battery made by Lucas marketed by Haze for £70 the Optima is £178 at 32AMP/HR. I know the Optima is a sturdy battery but do not think it gives any real advantage on the battery I intend to fit.
Checking with Haze manufacturer Haze gel and liquid AGM batteries are now fitted with external vent tube.

 

Agreed, its clearly cycles not hours. I was not necessarily trying to defend the Optima as the best choice, just stating that IMHO its the deep cycle capability (and resulting extended life) that's the main advantage not the capacity. If you can get a deep cycle AGM with greater capacity for less money in a brand you trust I'd say that sounds pretty good. The YT was attractive for me as I could get it all prepackaged in a kit with all the right connectors and fittings for the Prius for ~$150 at the time. At the prices you're seeing I think I'd look for alternatives too.

Rob

 

miscrms: In the chart you posted, I notice the number of cycles doesn't exactly go past ~5000 cycles
for DoD of <10%.

This seems to correlate with the following statements from the below mentioned page:

Deep Cycle Battery FAQ​

Capacity​

A couple of statements they make are:​

"​

Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%."​

​

"​

For longest life, batteries should stay in the green zone."​

​

The "green zone" in the second statement refers to 40% to 80% SOC.​

​

​

Read more: http://priuschat.com/threads/12v-battery-voltage-management.110449/#ixzz1xDlA9d4v​

My question is: wouldn't the low DoD of less than perhaps 5% hurt each time the system is started
hurt the number of cycles the battery can withstand?

 

Take a look at Ebay item no 270777983177
44% more capacity than the OEM, 86% more than the Optima and it's the same size as the OEM. I think thats good value.

 

The only way of knowing is by experimenting with yellow Optima or by asking Optima maker directly.

But if true, that would negate the value of deep cycle battery in prius. We know well that the starting batteries do best when DoD is very low (<5%). Maybe the red Optima is the way to go?

from:
Optima Product Support : Tech Tips

 

I've gotta throw in a curveball here:

Why not just use four 40152S Headway batteries for the 12V. The optimal voltage is 3.2 (3.2 X 4 =12.8). 15ah per cell =60ah. You can get these batteries for $24 each ($96 for a lithium 12V battery that fares better than both the Optima and the OEM on 100% DOD). Additional benefits are: lighter weight, smaller and no mods needed for charging. The current charging sytem wouldn't charge it above 95% (so you would theoretically never overcharge it).

Someone please tell me the errors of my thinking (preferably someone that's smarter than me (which pretty much includes everyone)).

 

When you connect cell in series the amp /hr capacity is the same as one cell = 15amp/hr not 60 as above, sorry.

 

Thanks Brit. I knew it was too good to be true. I guess the other alternative would be 8 40152S connected for a total of 12v output (2x2x2x2) for a price of $192 USD. This would be 30AH correct? Would that get the job done?

 

Yes that would work, but I think there is a further snag. If you discharge lithium batteries to far they become unusable, this problem may have been overcome but I'm not sure. Know doubt someone with more knowledge of these cells will chime in.

I think the battery I listed above would be better at 65amp/hr $178.

 

charging Li batteries is different from Pb, so I don't believe it would be a direct replacement.

 

The float charge voltage for these cells is 3.6v so x4 =14.4v at max 3C =45AMPS so the Prius system should be ok for charging.