[Jim_B]

When registering a new battery, the capacity in Amp Hours (Ah) is required. The Walmart battery we recently purchased (Maxx H8) is listed as having a capacity of 900 Cold Cranking Amps. The Walmart website lists the reserve capacity as '140'. (https://www.walmart.com/ip/EverStart...up-H8/16782659) Is there any kind of conversion from CCA to Ah? Or, are they two completely different measurements? (Like volts vs. watts.) Any recommendation for coding a battery with the capacity specified in CCA?

[Greyfox]

Some say it is

rc x .6 = ah

ie 140 x .6 = 84ah

others say its...

((rc x 60) x 25 amp) / 3600 = ah

((140x60)x25) / 3600 = 58ah

It's best to check with the battery manufacturer.

[mecheng77]

CCA is instantanous current, Ah is reserve power ie: 90Ah means the battery can deliver a reserve of 90A over 1 hour, or 45A over 2 hours etc..

I would call the battery mfg.

[Jim_B]

Originally Posted by Greyfox

It's best to check with the battery manufacturer.

Originally Posted by mecheng77

I would call the battery mfg.

Thanks for the replies!

It's a Walmart battery; I'm not sure who made it. Calling WM is, of course, less than useless. Even if I can find the manufacturer (Johnson Controls? Exide? Who knows? There could be several different suppliers.) I'm not sure they'd have/give me the information. I may do a bit of research to see what I can find.

I wonder if I can find a battery tester that could read the actual Ah capacity...

[Greyfox]

Originally Posted by Jim_B

Thanks for the replies!

It's a Walmart battery; I'm not sure who made it. Calling WM is, of course, less than useless. Even if I can find the manufacturer (Johnson Controls??) I'm not sure they'd have/give me the information. I may do a bit of research to see what I can find.

I wonder if I can find a battery tester that would read the actual Ah capacity...

I went to Interstate Batteries for my wife's car. Picked up an H7 which had the exact 80ah rating that I needed. It was worth the $50 over the equivalent Walmart battery.

[Jim_B]

Originally Posted by Greyfox

I went to Interstate Batteries for my wife's car. Picked up an H7 which had the exact 80ah rating that I needed. It was worth the $50 over the equivalent Walmart battery.

Good point, and I agree, but the battery is already bought/installed.

[Jim_B]

Some pretty good information in this thread: https://www.e90post.com/forums/showthread.php?t=1224488 There's also some info (some of it is conflicting) in the 'Questions' section at the bottom of the page on the Walmart website.

[Sgop335]

Originally Posted by Jim_B

Thanks for the replies!

It's a Walmart battery; I'm not sure who made it. Calling WM is, of course, less than useless. Even if I can find the manufacturer (Johnson Controls? Exide? Who knows? There could be several different suppliers.) I'm not sure they'd have/give me the information. I may do a bit of research to see what I can find.

I wonder if I can find a battery tester that could read the actual Ah capacity...

Did you get your answer?

Find it interesting that every other idiot in this forum uses your walmart battery and rave about it but dont know the Ah rating, which is the most important parameter for battery registration.
I think there are two battery manuf in usa, exide and deka or east penn. Deka has a great cross reference and so does exide. I purchased a napa battery recently, which is manuf by deka. It was a 100ah non agm battery. According to their site, the cross ref for maxxh8 ( assuming non agm) is 649mf - 100ah 185 rc 900cca. No guarantees but if exide manufactured the walmart battery chk their site.

[dpaul]

The reserve capacity is the number of minutes for which the battery can delivery 25 amps of current without its voltage dropping below 10.5

Convert reserve capacity to amp-hrs by multiplying by 0.416 (minutes x 60=seconds x 25 amps = coulombs / 3600 seconds per hour)

[Jim_B]

Originally Posted by Sgop335

Did you get your answer?

Find it interesting that every other idiot in this forum uses your walmart battery and rave about it...

I think there are two battery manuf in usa, exide and deka or east penn.

Deka has a great cross reference and so does exide. I purchased a napa battery recently, which is manuf by deka. It was a 100ah non agm battery. According to their site, the cross ref for maxxh8 ( assuming non agm) is 649mf - 100ah 185 rc 900cca.

Sorta, not really. In the 'Questions' section at the bottom of the Walmart website page, the Ah rating is listed as 80 in one place and 76 in another.

I'd say the Maxx batteries ARE actually really good. I've got one in my Subaru that was made in 2010 and it still works. (Yes, I know I should replace it ASAP.) That said, I would HIGHLY recommend to anyone reading this in the future to buy a replacement battery rated in Ah.

I think Johnson Controls also manufactures batteries, but I'm not sure and don't care to research it.

I have no why of knowing other than a semi-educated guess, but I doubt the Maxx battery has a 100 Ah rating. It's lead/acid (vs. the AGM 90 Ah stock batttery) and it's noticeably lighter in weight than the stock battery. (I didn't bother weighing either one.) Kinda hard to believe it would have a higher rating than stock but, again, I have no way of knowing.

[Jim_B]

Originally Posted by dpaul

Convert reserve capacity to amp-hrs by multiplying by 0.416

The reserve capacity of the Maxx battery is listed as 140. 140 x 0.416 = 58.24 It's a pretty big battery; kinda hard to believe the Ah capacity would be so low. (Not saying you're wrong, it's just that 58 seems low for that big a battery.)

[Welcome to NBA Jam]

There's not really a true conversion factor, but it is typically correlated with CCA and battery size.

[Jim_B]

BTW, a litte rant: In the future I would never buy another BMW, or any other car, that requires registering/coding for battery replacement. Funny how my SAAB, Subaru, GMC pickup and every other car I've ever owned/worked on doesn't require any software changes when replacing a battery. As I stated above, I've had the same battery in my Subaru for over 8 years and it's charging/working just fine. I've spent so much time on this battery replacement it's ridiculous...

[Jim_B]

Originally Posted by Welcome to NBA Jam

There's not really a true conversion factor, but it is typically correlated with CCA and battery size.

I was wondering if that was the case. Like how two appliances can have the same voltage rating, but different wattage ratings.

[dpaul]

Originally Posted by Jim_B

BTW, a litte rant: In the future I would never buy another BMW, or any other car, that requires registering/coding for battery replacement. Funny how my SAAB, Subaru, GMC pickup and every other car I've ever owned/worked on doesn't require any software changes when replacing a battery. As I stated above, I've had the same battery in my Subaru for over 8 years and it's charging/working just fine. I've spent so much time on this battery replacement it's ridiculous...

Apparently, as long as you are replacing the old battery with one that has the same parameters, neither coding nor registration are necessary.

There is an interesting discussion of the issue here (see post #27 and #31 by gbalthrop):
https://www.e90post.com/forums/showt...php?p=24376332

[Jim_B]

Originally Posted by dpaul

Apparently, as long as you are replacing the old battery with one that has the same parameters, neither coding nor registration are necessary.

...and if it's a different capacity/type it's a colossal, time-wasting PITA. (Both coding AND registration are required.) Odd that it has an 'Intelligent Battery Sensor' but it still needs to be told what to do.

[dpaul]

Originally Posted by Welcome to NBA Jam

There's not really a true conversion factor, but it is typically correlated with CCA and battery size.

The formula I provided may not be "true" but it is "real" i.e. based on simply physics and the assumptions built into the definition of "reserve capacity"

Perhaps some of the problem stems from our definition of terms. Reserve capacity is commonly defined as minutes with 25 amp draw down to 10.5V.

I'm not sure that "amp-hour" has any formal parameters attached, which could be why manufacturers of car batteries seem to avoid taking about it. Like RC, it will vary significantly depending on the magnitude of the current being drawn and the acceptable final terminal voltage.

Finally, I'll guess that the correlation of CCA with RC (or amp-hour rating) is not particularly dependable. CCA is most strongly affected by the internal resistance of the battery and can be quite different in two batteries of different construction with similar reserve capacities.

[gurusan]

I'm sure the actual manufacturer should be somewhere on the battery?

[dpaul]

Originally Posted by Jim_B

...and if it's a different capacity/type it's a colossal, time-wasting PITA. (Both coding AND registration are required.) Odd that it has an 'Intelligent Battery Sensor' but it still needs to be told what to do.

It is a classic example of German under-overengineering!

[dpaul]

I require medication after the effort needed to get that stupid ass fuse holder off the top of the battery so it can be changed

[ctuna]

group 49/H8 battery's seem to all be in the 95 to 110 amp hour
range.

[Sgop335]

Originally Posted by Jim_B

That said, I would HIGHLY recommend to anyone reading this in the future to buy a replacement battery rated in Ah.

don't have to twist my arm. That is why I didn't buy the maxx battery, because I would like to see its Ah rating. It may be a fine battery.
also what ctuna says above has been my observation as well...