Walmart 27DC….80 or 109AH?

[mooky_stinks]

I ordered 2 27DCs from the Walmart website yesterday. The description stated an amp/hr rating of 109. When I picked the batteries up they had hold stickers on top with my name etc. When I got them home and peeled the stickers off they had a rating of 80 amp hours @ 20hr on the label. They do weigh what the description states @ 50.2lbs each. I’m pretty sure Johnson Controls were making batteries for them and they have been bought out by Clarios? I’m not familiar with this 20hr style of rating either. There is some mention of this in some of the reviews but nothing more than someone returning the batteries for this reason. Did I get what I wanted or is there something more to this?

[valhalla360]

KD4UPL wrote:
it's called the Peukert effect

This is the answer.

Basically, the higher the amp draw, the lower the amp-hr you can expect. Therefore, they need to define the amp-hrs in terms of the draw. 20hr rate is basically 5% of amp-hr rating which is fairly reasonable for a house battery.

[mooky_stinks]

Thanks to everyone for the info! I learned something today.:C

[Skibane]

KD4UPL wrote:
Basically their marketing guys used a non standard number to make the advertising look better. It's not wrong, just a little sneaky.

If they used a 0.001 amp load, they could probably get 150 AH out of it! :B

[KD4UPL]

Just about all Group 27 batteries are, give or take, about 75 amp hours. Yours are 80 so that's on the upper end. Rating them with a 20 hour draw is the industry standard.
A manufacturer can rate them at any draw they want for marketing purposes. Apparently yours are about 109 AH at what is roughly a 100 hour rate. I suspect if you tested them at an 80 amp draw you might only get 1/2 hour making them 40 AH at that rate.
All the numbers are correct, it's called the Peukert effect if you want to read all about it.
Basically their marketing guys used a non standard number to make the advertising look better. It's not wrong, just a little sneaky.

[Skibane]

mooky stinks wrote:
I did just look at the website photo of the battery and it shows on the label: 109 amp hrs @ 1 amp
VS what I received which states 80 amp hrs @ 20hrs. I can’t find anything that states if these two ratings are just a number game or they truly are different.

It's the same battery, just being tested with two different loads.

At higher loads (i.e., more amps), the battery has less effective capacity, because higher loads cause more of the battery's power to be wasted as heat. With more power wasted as heat, less power is available for whatever you're powering.

[2oldman]

All deep-cycle batteries I've seen are rated nominally at 20 hours.

[red31]

from a JCI 2003 spreadsheet showing amp hours vs constant draw down load

[BFL13]

20 hr rate is 4 amps If you draw it down at 1 amp it lasts longer Not a scam, but a sales trick to use the 1 amp rate

[mooky_stinks]

I did just look at the website photo of the battery and it shows on the label: 109 amp hrs @ 1 amp
VS what I received which states 80 amp hrs @ 20hrs. I can’t find anything that states if these two ratings are just a number game or they truly are different.

[Lwiddis]

Twenty-nine amps is significant when talking about totals of 218 vs. 160. I’d return them and ask for what was advertised. Take your written proof.

[MNRon]

If the sticker says 80AHr, that's probably what you got. 20hr run down rate is typically how batteries are classified for capacity, things like 'cranking amps' don't apply for camping use. If you're installing two, you'll probably get more capacity (as well as battery design robustness) by installing two 6v golf cart batteries in series. Sams and Costco seem to have the best deals on these typically.