Good deal on deep cycle gp 31's?

[Tenor]

I just picked up 2 blemished gp 31 lead acid dry cells from Interstate battery for 39.95 plus core.  They have a 105 AH rating.  My long term plan has been to get 2 AGM 8D's to use with my Xantrex 4024.  Those would give me around 220-250 AH.  I'm wondering if I should just grab a bunch of these and build a box.  It takes 4 of these gp 31's to come close to the AGM 8D's.  I know that the maintenance differences, and the speed of recharge, but the dollar signs are real tempting.  What does anyone think?

Thanks!
Glenn

[gumpy]

I haven't priced them lately, but a few years ago, Trojan T105s were going for about twice that. They are 220 ah at 6 volts.  Having just bought a new 8D starting battery for the bus, and another Gp31 for a backhoe, I know batteries are higher now than they were a few years ago.

I have the SW4024 in my coach, and I run 8 of the T105's.  I can go about 2 days if we're careful before I need to recharge.

If you're planning on boondocking for extended periods, I think the 105 ah battery might be a bit small.  If you are only overnighting or short periods off shore power, then these would probably work ok.

craig

[Tenor]

Craig,
How many T105's are you running?  I know you need at least 4, but are you running 8 to bump up the AH to 440?  With these, I could get 210 AH with 4 gp 31's, and 420 AH with 8 gp 31's.  8 batteries would run me $320 plus core.  ( I did buy two already to get me through a few overnights over the next couple of months). 

On a side note to you, I just was given a bunch of garage door track and rollers.... 

[PP]

Glenn,
I just replaced 4- 6V 225AH that were just over a year old and dead beyond recovery due to overworking them. If I had the chance to buy gp31's for that price, I'd have jumped at them and made room for 4 more. That's my .02 worth, Will

I forgot to add-I'm assuming they're deep cycle bats?

[edroelle]

Glen,

Are you sure that these are deep cycle?   You need to use deep cycle for your house batteries, not starting batteries.

Did you really mean they are "dry cells"? 

Ed Roelle

[Tenor]

Yes, these are the deep cycle group 31's.  I see I had a typo in the subject and I've fixed that.  Sorry for the confusion. 

Glenn

[Sean]

Glenn,

Do you have a part number on these?  I just tried to look them up for you, but I don't see any deep cycle flooded Group 31s on Interstate's product list.

-Sean
http://ourodyssey.blogspot.com

[Tenor]

http://www.interstatebatteries.com/cs_estore/content/product_info/marine_f.asp
They list thsese as group 29, but they have the same exterior dimensions as group 31.  Whayt do you think?


Thanks!
Glenn

[Sean]

Glenn,

The Interstate SRM-29 is not a true deep-cycle battery.  It is a "marine" battery, a hybrid where they have attempted to strike a balance between cranking ability and "deep cycle" ability.  These types of batteries excel at neither task.

Unlike a true deep cycle battery, which can routinely be discharged to 80% DoD, these batteries should never be discharged below 50%.

Personally, I don't think they are worth the headache, even at that price.  But everyone has a different price/headache tripping point.

A good 8D AGM (chosen only because that's what you mentioned) will have about 220-230 AH, of which around 80%, or 180 AH, is usable.  You'd need 3.5 of these Interstates to equal the usable capacity of one of those AGMs.  That's $140, assuming you have 3.5 trades, vs. about $400 for the AGM.  A  significant saving in dollars (but not space or weight) if you want to hassle with them.  The other thing to remember is that a pair of 8D AGM's will require two battery jumpers (for a 12-volt system), whereas seven of these batteries, to get the same capacity, would require 14 jumpers, somewhat reducing your savings.  If you also bought six HydroCaps for each battery, it would likely wipe out the savings altogether.

FWIW and YMMV.

-Sean
http://ourodyssey.blogspot.com

[gumpy]

Craig,
How many T105's are you running?  I know you need at least 4, but are you running 8 to bump up the AH to 440?  With these, I could get 210 AH with 4 gp 31's, and 420 AH with 8 gp 31's.  8 batteries would run me $320 plus core.  ( I did buy two already to get me through a few overnights over the next couple of months). 

On a side note to you, I just was given a bunch of garage door track and rollers.... 

I run 8 T105's.  If you can get 440 ah from 8 of those, it might very well be a good deal (or maybe not, now that I've read Sean's post 

Garage door track...  I had to abandon my battery rack last year when I moved my electrical to install my genset. But it worked well for me for a few years.

[Tenor]

Thanks Sean!  That's about the same figuring I came up with, except that I'm running a SW 4024, so I need 2 of the AGM 8D's, or 8 of these others.

Craig - I read that you realized some design issues with the first rack.  I love your site!

Thanks!
Glenn