0

I just got a group 29 duralast marine deep cycle battery from auto zone. The group 29 is the first link below. I got it home and looked online and found that the group 29 battery weighs 10 pounds more than the group 27 battery and the group 29 had 20 amp hours less power than the group 27. I wanted to use this battery as a backup for my 1/4hp sump pump and also for a 56 ft-lb electric trolling motor so I really value a higher amp hour over startup cranking amps. I was wondering if there was possibly a typo on their website or if a larger battery could indeed have less amp hours of power.

Group 29 battery - https://www.autozone.com/batteries-starting-and-charging/rv-battery/p/duralast-29dp-dl-group-29-deep-cycle-marine-and-rv-battery/95824_0_0

Group 27 battery - https://www.autozone.com/batteries-starting-and-charging/rv-battery/p/duralast-27dc-group-27-deep-cycle-marine-and-rv-battery/315062_0_0?cmpid=LIA:US:EN:AD:NL:1000000:DBA:10620994470&gclid=CjwKCAiAvOeQBhBkEiwAxutUVLlKkN0vfIZ9wjgXAuBHdTo0ziq81qmMHaBib3NIteetcmo3NY93YhoC1U4QAvD_BwE&gclsrc=aw.ds

Improve this question
4
  • Hard to say since they don't reveal the rate for the AH - easy to get More AH from Less battery if one is rated at 20hours and the other is rated at 100 hours - the longer the time, the more Ah you can pull (at low Amperes, because that's how lead-acid batteries work in real life - high draw lowers the capacity, low draw increases it even for the same battery. But there's no mention of the rate for either battery.
    – Ecnerwal
    Commented Feb 27, 2022 at 0:35
  • According to the website, it says the group 29 is 65 Amp hour and the group 27 is 85 Amp hour which really doesn't make sense to me. The group 29 should have more power since it is bigger and weighs 10 more pounds.
    – Justin Todd
    Commented Feb 27, 2022 at 2:13
  • Why not weigh the battery you have and at least verify that spec?
    – Armand
    Commented Feb 27, 2022 at 6:35
  • Weighed the battery and that spec is accurate
    – Justin Todd
    Commented Feb 27, 2022 at 17:59

1 Answer 1

Reset to default
3 
Weight  59.66lbs
Marine Cranking Amperage    840A
Negative Terminal Location  Top Right
Reserve Capacity    210min
Positive Terminal Location  Top Left
Amp Hour    65Ah

.vs.

Weight  48.62lbs
Marine Cranking Amperage    840A
Negative Terminal Location  Top Right Front
Reserve Capacity    130min
Length  12.0625in
Positive Terminal Location  Top Left Front
Amp Hour    85Ah

Yeah, something doesn't add up. "Reserve Capacity" is how long they can deliver 25A for at 80F if fully charged, while staying above 10.5 volts.

For the first battery, that's 210, which equals 87.5 AH (at the 3.5 hour rate) yet somehow the (presumably) 20 hour rate is only 65 AH.

For the second, it's 130 which equals 54.17 (at the just over 2 hour rate) and that, as expected, is less than the (presumably) 20 hour rate of 85.

There are certanly ways in which a heavier batter can have less capacity, usually due to incrasing some other quantity, but here the cranking amps are the same, and the two capacity specs conflict. You'd have to ask the manufacturer what's correct.

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.