Difference between group 31 and 29 deep cycle batteries

airshot

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My house battery died over the weekend so looked for a replacement. It had a group 31 deep cycle so I did some research. Wow....no clear explanations even going years back. Was comparing group 29 to 31. I soon became confused, I am a retired toolmaker, I can make anything but no where near an electrical genius...After many worthless explanations that counterdicted each other, I just bought the battery for the best price. When my trolling motor batteries dieoff, I will consider going LifePo4, but for just a house battery for electronics a regular flooded cell is fine, never have I ran a house battery dead, don't use that much power.
I ended up with a group 29, same size as my group 31, same amps as the group 31 sitting next to it, in fact all the tech numbers were the same. Weight felt the same just by lifting, however the 29 was twenty bucks less. What am I missing between these two sizes ?? Even the warranties were the same, two yr replacement. Any electrical wiz's that might shine some light on the differences ?? Thanks...
 

Scott Danforth

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Look up the BCI dimensions. There are differences in length, width, and height between a group 29 and a group 31
 

silverbul

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Also group 29 batteries have a shorter life span than group 31 batteries. They typically last for about 500 cycles, while group 31 batteries can last up to 800 cycles.
 

airshot

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I was in Walmart, they had both, plus, I had my 31 in the cart as a core. The 29 and 31 batteries were side by side on the shelf, now...I didn't have a set of calipers with me, but as a toolmaker with over 50 yrs in the trade, I am very good with measurements. Setting the two (31 & 29) they could not be off more than 1/16" in any direction. Batteries were clearly marked on the plastic body, not someones writing, as a 29 and a 31 group size. Tried Auto Zone and O'Reilys and my old 31 was a match in size to their 29's. Most all battery stats matched on both sizes. Just lifting by hand they seemed to weigh the same, I would know if there were 10/15 lbs difference. This is where the confusion comes in. Spent a few hours researching differences on the internet, even more confusing !! I finally decided to save twenty bucks on the 29, took it home and it just fits in the 31 box with very little room to spare...less than a quarter inch of space anywhere. Confused as ever !!
 

Scott Danforth

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lenth is within 1/8, width is within 1/16, height is 5/16" different

batt.jpg
 

dingbat

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The difference between the two is physical size only.

Amp hours is a function of plate density. Both weighing the same is the give away.
 

airshot

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Well, I have experienced an eye opener here. Are mfgrs just trying to get a few more dollars out of consumers??
With matching specs why spend more for a 31 size when a 29 gives tou the same power. Not saying that more expensive batteries might make a big difference but economical batteries....no difference except cost.
Thanks to all that responded...
 

dingbat

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Well, I have experienced an eye opener here. Are mfgrs just trying to get a few more dollars out of consumers??
With matching specs why spend more for a 31 size when a 29 gives tou the same power. Not saying that more expensive batteries might make a big difference but economical batteries....no difference except cost.
Thanks to all that responded...
Ran into a similar situation last Spring with Walmart when I replaced both Everstart 27DC batteries after 10 years of service.

In shopping around I noticed the price on the 27DC had dropped a good bit. Dug into it a bit and found the amp hour rating had dropped going from 109AH to 86AH. On top of that the battery now sported a MCA rating.....obviously changed the construction from Deep Cycle to Dual Purpose. ;(
 

airshot

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Ran into a similar situation last Spring with Walmart when I replaced both Everstart 27DC batteries after 10 years of service.

In shopping around I noticed the price on the 27DC had dropped a good bit. Dug into it a bit and found the amp hour rating had dropped going from 109AH to 86AH. On top of that the battery now sported a MCA rating.....obviously changed the construction from Deep Cycle to Dual Purpose. ;(
Yes....agree whole heartedly, when shopping for economical batteries look carefully, things change and not always for the better !!
 

Grub54891

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I'm just thinking outside the box here. You could have went to the homeware dept and borrowed a scale, weighed both batteries and see if there is a difference. I've done similar things when at the store comparing items, Forgot to bring a tape measure? they have them in the tool section.
 

airshot

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I'm just thinking outside the box here. You could have went to the homeware dept and borrowed a scale, weighed both batteries and see if there is a difference. I've done similar things when at the store comparing items, Forgot to bring a tape measure? they have them in the tool section.
The difference is so small it would take a measuring tool to tell the difference. Sitting side by side and end to end there was no noticible difference. According to the stats, one weighed 58 1/2 lbs and the other weighed 59 1/2 lbs. Hardly a difference, but the tech specs were identical, amps etc. Saved $21.40 buying the 29 size and getting the same power !! When my trolling motor agm's bite the dust, I will switch over to a LifePo4 100 amp, but for a house battery, the regular ole flooded cell lasted for over 5 years at 1/3 the cost. Don't really use much house power, fish finder, aerator for minnow bucket, radio and on ocassion the running lights. Went out 4th July night, gps, radio, lights with interior lights for over 4 hours battery dropped from 12.8 down to 12.6 so plenty of power. Usually get 2-3 fishing trips before battery gets down enough to even think about charging it back up.
 
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