Mixing batteries

S

Steve OD

Member
Oct 26, 2017
70
West Yarmouth, MA
Boat Info
Sol Searchin'
1996 330 Sundancer
Engines
7.4 L V Drives
I have 4 Interstate 27 batteries, 2 of which will not hold a charge. They are only 3 years old.
I want to replace those 2 with 31's. (Sam's club, $99 each)
Is it ok to have 2 27's and 2 31's?
If so, would I keep them together, 2- 31's on port side and 2 -27's under the rear facing seat or mix them?
Thanks and stay safe!
 
As long as you replace paired batteries together, you are good with a 27 to 31 swap. While $99 is a great price, SAMs was selling GRP 31 AGMs for $165 - an even better deal - IMHO...
 
Steve OD said:
I have 4 Interstate 27 batteries, 2 of which will not hold a charge. They are only 3 years old.
I want to replace those 2 with 31's. (Sam's club, $99 each)
Is it ok to have 2 27's and 2 31's?
If so, would I keep them together, 2- 31's on port side and 2 -27's under the rear facing seat or mix them?
Thanks and stay safe!
Click to expand...
Yes to both
 
carterchapman said:
As long as you replace paired batteries together, you are good with a 27 to 31 swap. While $99 is a great price, SAMs was selling GRP 31 AGMs for $165 - an even better deal - IMHO...
Click to expand...
I was thinking of that, but then would have to replace all 4 and update my charger
 
Steve OD said:
I was thinking of that, but then would have to replace all 4 and update my charger
Click to expand...
Steve, my older chargers always worked fine with AGMs - same settings. GEL batteries are the ones that need different settings. While some of the newer chargers have a setting for AGMs, the AGMs on my former 340 are 10 years old and still going, on my former 410 they are 8 years old and still going - both with an older charger on the lead acid setting...

So...I would think you'd be OK changing one pair at a time and mixing a pair of each since older chargers treat AGMs as lead acid batteries...

The AGM in my waverunner is 12 years old, still going, and my XLR that I don't drive in the winter has one that is 12 years old...
 
Steve OD said:
I was thinking of that, but then would have to replace all 4 and update my charger
Click to expand...

FWIW updating your charger is a pretty decent idea at any rate, and a very easy install. My '97 vintage charger cooked a perfectly good battery last summer. A new ProNautic charger is $500 well spent. If your luck is anything like mine your existing charger will take a crap right after you buy a bunch of new batteries :)
 
If 2 of the 4 are already bad, I think you'll be lucky to get another season out of the "good" set of 27's.

The difference between a flooded and AGM charge schedule is fairly small and you could likely get away using a mix of AGM and flooded off the same charger for a season. Do the 2 Group 31's now to get you going. You know you'll need to replace the other 2 soon, so budget for that. Lastly plan to replace the charger possibly in the off season.

Same amount of money, but broken down into 3 smaller chunks.
 
dtfeld said:
If 2 of the 4 are already bad, I think you'll be lucky to get another season out of the "good" set of 27's.

The difference between a flooded and AGM charge schedule is fairly small and you could likely get away using a mix of AGM and flooded off the same charger for a season. Do the 2 Group 31's now to get you going. You know you'll need to replace the other 2 soon, so budget for that. Lastly plan to replace the charger possibly in the off season.

Same amount of money, but broken down into 3 smaller chunks.
Click to expand...
Sounds like great plan, thanks everyone for the input!
Hopefully I'll get her in the water next week, if it stops raining up here!
 
This is great info. Don’t want to switch all 5 to agm at once, but I could see doing 2 on one bank, then next year 2 on another bank, and lastly the genny battery. I do have an updated smart charger

thank you for this post!
 
Changing over to AGM’s one bank at a time, followed by the generator battery is my plan.
Nice way to spread the cost.
I’ve got a 2017 battery bank, and the other bank and genny are 2018 replacements.
I’ll probably replace the 2017 batteries with AGM’s next year, the other bank the following year and the generator battery the year after that.
 
I'd replace all and they should be good for five years.
 
Brite Idea said:
I'd replace all and they should be good for five years.
Click to expand...


That would be ideal, but 5 G31's and a new charger are $1500!! Thats a lot of $$$$. Great if you've got it or budgeted for it, but we all know we need to plan and spread the expenses.
 
As a follow up, I went to Sams to get the batteries the website said were in stock, but they were not, and are not currently getting deliveries.
I went on the website to check other stores and the next closest club (30 miles away) has AGM 34's (in stock!) on sale for $119!
Is this too good to be true?
 
Steve - I don't have a need for GRP 34's. so I've probably forgotten more about them then I ever knew, but I think while 27's and 31's are close in specs, 34's are quite a bit lower in CCA's, et al.

I'll let one of the electrical genius' step in on that, but Google may answer that for you...
 
Group 34's are much smaller batteries, closer to a group 24 (I think same footprint, but the 24's are 1" taller?) and about 50-60 Ah, were as the Group 31's AGM are around 105 Ah, so about 1/2 the storage.

On thing to consider, it that the way Sea Ray set your batteries up, may not allow a new type battery to be installed without re configuring the cables/terminals...

With that said, if you can get 2 31's in the same spot..its a very good upgrade in terms of power reserve, and battery longevity!!
 
I researching prices for these batteries, I came across this at Batteries Plus
10% off when you order online and $10 mail in rebate.
Same batteries I bought at Sams for $179 are $129 before discounts and rebates.
But, in the description line, it says not ideal for starting main boat engine
  • 12 Month Free Replacement Warranty
  • Best for boat deep cycle applications and accessories, plus RV use
  • Handles demands of trolling motors, fish finders, GPS systems, and radios.
  • Designed to provide extended power and battery life while on the water
  • Not ideal for starting main boat engine
  • 105 amp hour capactiy to keep your boat on the water longer
Any idea why?
Thanks
 
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