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-   -   AGMs or 8Ds.... (http://www.wakeworld.com/forum/showthread.php?t=780419)

tdc_worm 06-09-2010 8:50 AM

AGMs or 8Ds....
My stereo overhaul consists of the following amps:
3 x Zapco Ref 1100.1
1 x Zapco C2K 9.0
Xantrex Truecharge2 40 amp charger

I am tossing around a couple of options for power. I have come across deal on some Sprinter (made by Exide I believe) AGM batteries for $70 each. Supposedly 110-120 amp hour capacity, built in 2008, and have been on a float charge ever since. No warranty, pro rated or otherwise.

Option 2 would be 2 x 8D batteries, w/ 435 minute reserve capacity each at 25 amps. They are around $180 locally, plus $10 core, plus taxes, so figure around $410, but they do have a warranty.

I am not sure how amp hours converts to reserve capacity and visa versa to ensure that I we are comparing apples to apples in terms of # of AGMs vs. 2 x 8Ds.

Each has their pros---flexibility with location in boat and w/ AGMs and ease of install, warranty (i.e. less cable and connectors) for 8Ds...

Each has their cons---no warranty, more cable routing, battery boxes, etc for AGMs and individual weigth and location restrictions due to size for the 8Ds

What other considerations are there here? What would you do?

acurtis_ttu 06-09-2010 11:14 AM

dependig on location of the batteries, if cost is a concern, you can't beat the 6v golf cart route IMO.

xxxChrisBxxx 06-09-2010 11:21 AM


hatepain 06-09-2010 11:36 AM

Who makes the 8D's? Thats really cheap for that much battery. It's been hard but I've managed to get mine out of the way pretty well. If you put two good 8D's in your boat you'd be hard pressed to beat them. They should have an amp hour rating on them for instance my Lifelines have 255.

tdc_worm 06-09-2010 1:59 PM

about the golf car batteries---i can source group 31 AGM batteries w/ 110-120 amp hours each for about $70 per battery...advantage AGM (I have run GC batteries before...)

about kinetiks---i can get way more AH for way less money that kinetik...re read my post and you will see to two proposed routes

Hate--->they are branded Rayovac and sold by batteries plus...i think they are made by deka. the reserve capacity is 430 minutes at 25 amps. its a different way measuring capacity...check this sight: http://www.dcbattery.com/faq.html#3

i thought i read somewhere that AGM batteries hold a higher float charge and are more durable than other batteries...thoughts?

hatepain 06-09-2010 2:31 PM

I'm not sure how the two relate but mine are rated for 475 reserve so they may be close in AH. My Life lines are AGM and if Deka makes those they are likely AGM as well. AGMs can take a beating, can be mounted any which way and can be discharged and charged about twice that of standard.

humboldtboarder 06-09-2010 3:01 PM

I believe that a 120 amp hour battery would be about 288 minutes reserve capacity at 25 amps. 120ah/25a=4.8hours 4.8hx60= 288minutes @ 25a I'm not for sure that is how you do the conversion, but that is how it was explained to me. So if you are comparing 4 of the AGM's to 2 8D's, I would say the AGM's win for sure.

tdc_worm 06-09-2010 3:16 PM

nick--->i havent had time to sit down and crank out the conversion, but that looks reasonable. of course, all of that changes according to temperature, current draw, and how much the battery is charged.

hate--->i do not believe these 8ds are AGM, i think they are flooded cell... here is very non specific link: http://www.batteriesplus.com/p-36528...er-sli8da.aspx

it seems that the a handful of the Group 31 AGM batteries is the way to go...the only catch is that there is no warranty...

hatepain 06-09-2010 3:57 PM

Yeah those definetly fall short of the Lifelines probably the reason they're a fourth the price. I'm not so sure that is how the conversion is done as my batteries have 255 AH and 475 reserve. Based on that math I should have over 600 reserve. There are some smart battery guys on here that may know.

05mobiuslsv 06-09-2010 5:46 PM

I don't think there is a battery out there that can take a beating like the golf cart batteries can. I've tried them all. Had 5 optima's and two of them went bad on me. Had a Lifeline 8d AGM battery that took a crap on me. I charged all of these with a 3 stage smart charger. Went to interstate 6v batteries and so far so good.

hatepain 06-09-2010 6:42 PM

It's true golf cart batteries are designed to be run down and brought back time and again. Nu, how many volt charger were you using on your 8D? If they get beat down it can take a lot to get them back up to snuff.

05mobiuslsv 06-09-2010 6:47 PM

It was a 4/10/20/40 selectable, I used the 40. It never really got run down very far, I never did the party cove with that battery. I hope you have better luck than I did. The battery didn't die it just lost half it's capacity so it drains really fast even though it says it's charged 100%.

humboldtboarder 06-09-2010 8:15 PM


Originally Posted by hatepain (Post 1595146)
Yeah those definetly fall short of the Lifelines probably the reason they're a fourth the price. I'm not so sure that is how the conversion is done as my batteries have 255 AH and 475 reserve. Based on that math I should have over 600 reserve. There are some smart battery guys on here that may know.

Looked into the conversion a little more and came up with AH = (RC / 2) +16 So that would put the AGM's at around 188-208 reserve.

humboldtboarder 06-09-2010 8:27 PM

I think it was Mikeski that recommended looking at the weight of the battery to determine capacity. I noticed the Rayovac 8D lists a weight of 126lbs. Lifeline lists their 8D at 162lbs. That quite a difference. It would be interesting to see what the AGM's you're looking at weigh and compare the $ per lb.

tdc_worm 06-10-2010 7:12 AM

The S12V370 AGMs are 74 lbs...and appear to be a group 27 size battery as per this PDF: http://www.staticpower.com/pdf/SprinterS_t_e.pdf

The document just gives power ratings in watts per cell, not in amp hours or reserved capacity. Using 100 Ah that would put them at 1.35lbs/Ah and using 120 Ah, they would be 1.621lbs/Ah. Compare that to Hates AGMs----his some in at 1.547lbs/Ah. Is it reasonable to assume that (using Mikeski's thoughts and Hates data) that these batteries are truly somewhere around 110Ah or just a little more?

05mobiuslsv 06-10-2010 7:38 AM

A group 27 battery is typically 100-110 amp hours.

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