Optima AGM Batteries

quique

Hi,

Im looking at batteries. The market is very limited here and what Ive been offered are:

1) Optima Blue Top Model D31M-900. I looked up the specs on their site and I get

Capacity: 75 Ah (C/20)
CCA (BCI 0°F): 900 amps
MCA (BCI 32°F): 1125 amps
Group Size: BCI31

Im trying to relate this to the AH capacity I need. Ive read that depending on the way manufacturers rate batteries (@100hrs or @24hrs) their AH rating might be higher or lower. I can see ...

2) Deka Marine Master DC31T

Im assuming its DC-31DT because on the quote it reads Deep Cycle

20 AH Rate: 105
CCA (0F): 650
MCA (32F): 850
Group Number 31

Im guessing what I need to compare is Optima's c/20 rating of 75 against Deka's 20 AH Rate of 105?

So in that sense, DK would be better? What about CCA & MCA?

inetdog

Re: Optima AGM Batteries

CCA and MCA are both related to engine cranking (i.e Cold Cranking Amps, etc.) and are not really relevant to deep cycle use.
To some extent if two batteries have the same AH rating (C₂₀), the one with the LOWER cranking performance will probably be better for deep cycle.
But any battery that lists MCA or CCA is not really an RE-optimized deep cycle battery. It is more properly called a hybrid or dual use battery.

Do not trust the seller's wording "Deep Cycle" if the model number does not match that given by the manufacturer.
The DC weighs 2 pounds more than the DP, probably all in more lead in the plates, which is good.

The reference to "20 AH rate 105" is bogus and a bad sign about the seller. The correct value is probably 105AH, 20 hour rate, but I would not take that for granted. The manufacturer's site correctly shows "20 hour capacity" of 105AH.
But based on the relationship among the three numbers, I would say the Deka is better, as long as the 31DT is what you really get.

An even more important difference though, is that the BlueTop is an AGM battery and so is capable of lower internal resistance with higher current, but it is a sealed battery which will not last as long and may cost more. Most importantly the BlueTop series is NOT recommended by Optima for RE or other deep-cycle use. Try their YellowTop instead for that purpose if you can get it.

PNjunction

Inetdog - sorry about the 2-year followup!

Sure enough - Optima, like all dual-purpose batteries, are only "deep cycle" when compared to SLI or starter equivalents. Compared to a T105RE, no way. But the 12v guy can work with them (no red-tops) when we treat them properly.

Most importantly the BlueTop series is NOT recommended by Optima for RE or other deep-cycle use. Try their YellowTop instead for that purpose if you can get it.

ALL Optimas are built the same physically with of course different capacities. The only thing that differentiates their SLI vs deep-cycle (so called) is that that the SLI/Starting versions have a higher acidic content and slightly different paste material for better starting power. The SLI/Starting versions come in BLACK cases. Most are red top with black case, but there is also a so-called "marine" which is a blue-top with black case. All starting and high acidic content.

The so-called deep-cycle Yellow tops and Blue Tops come with a light-gray case. They have a less acidic electrolyte - EXCEPT for the one model of the blue that has a black case for starting. So other than that, the only difference between the yellow and blue top models are that the blue's have convenient threaded lugs in addition to the lead posts. The yellows have more options in side-connectors depending. But basically, except for the black-case model blue top, the yellows and blues are the same.

Thing is, we never REALLY do deep-cycle! Most solar calculations as described here wisely only take them down to 50% DOD. What Optima is thinking is total discharge, and not educated solar guys that only go down to 50%.

Like all "pure lead" agm's, such as Odyssey, Lifeline, etc, they really benefit from the low internal resistance. While the average solar guy who is not trying to race these cells to death may not see an immediate benefit, that lower internal resistance means much less time charging, and especially during the absorb phase, which is crucial for solar life to try and finish if the application is very cyclic.

I know, too much info. But if you have an Optima, you CAN do solar with it properly, even though Optima does not go out of their way to officially support it.

Basically, avoid black-case starting versions, and then choose whatever color yellow/blue with light-colored case that you like that meets your connectivity needs.

PNjunction

Additional field notes about Optima and solar

Keep in mind that some solar projects with Optima's have failed due to prior abuse. That is, I've visited some sites with projects complaining about performance, when the fact was that they started with a 4 year old Optima, that sat under the hood in Arizona for a few years, and never ONCE got a proper full charge - mostly due to infrequent short Starbucks runs in the Ford 4x4 and got the battery pulled for the solar project. That's a problem for any battery.

When starting a new project, with a new Optima they aren't living underhood. They won't be discharged more than 50% DOD. They should have a minimum charge current of at least 0.1C, preferably more, and voltages like 14.4 - 14.7v absorb will be easily attained by a quality charge controller. Things are looking up to at least meet their "hybrid" or "dual-purpose" cycling specs. For some, the battery might age faster than the cycle count does.

BUT an additional warning - most of these batteries are obtained at a nearby auto-parts store. And as such, have cheap automotive-type chargers that in some cases, do a lot of damage to a battery that only needs a charge, and NOT total resurrection from prior abuse. Many of the chargers that have the "Speed" labeling have done this to my batteries, despite the so-called "smarts". I am not fond of Schumacher chargers for batteries that don't need resurrection, although some worked ok. I like to track charging paramaters with my own gear. I moved on.

Optimas are only ONE choice of battery and are not the only ones I use, so no favoritism here. But I wanted to toss this out since they are so widely available that I see them often in solar projects I visit - mostly new experimenters. They do fine, but not if they have been previously abused - so starting out on the right foot, especially for new users, is important.