The deep cycle lifeline agm can be cycled 1000 times while the trojan 105 500. The argumernt more bang for your buck does not really apply as you have to replace the trojan batteries once to equal the lifeline agm thus equalizing their price.
Sadly the realities of marketing claims have not come through in the real world as I have seen it with AGM's. My friend Dave is a battery distributor and sells/distributes Lifeline, Trojan, Deka and many others. When I ask him about AGM longevity vs. deep cycle wet cells he just smirks and chuckles, then I hear something like "on paper blah, blah, blah...BUT"
Just last week he had no less than 20 AGM batts on core pallets. The oldest date code of the 20 +/- AGM's was 6 years, but the average was under 5 years. I look at the pallets and dates, as I have been, since my buddy Tom's premature failures of Lifeline's. Dave also had a fair slug of Trojan's and other deep cycle golf/industrial batteries. The average date codes on the deep cycle wets were 6+ years.
In my own personal experience I have not seen anywhere near the length of service the AGM makers claim. There are numeraous complaints on the many sailing forums of short lived AGM's despite proper care and feeding.
I installed 6 Lifeline batts on my friend Tom's boat, along with a gourmet charging system to match it. Nearly 3.5k worth of upgrades in just material costs.
Everything was done to Lifeline's requirements, charge profile, winter storage, float, absorption etc. etc.. Tom babies his batteries and treats them better than I do yet last spring he brought them over to me asking what I thought was wrong?
Took them over to the distributor and they were DEAD. Called Lifeline and was told this in not unusual and that he got a good service life? Really? He had nowhere near 1000 cycles, not even 500..?
His previous bank was T105's on a dumb regulator and fero charger and they lasted him 8 years and were still going strong when he made the change to Lifeline's. I have personally seen more than one bank of Trojans older than ten years and still going. Perhaps we will see this with AGM's but I have yet to.
I have yet to see many AGM's live up to the claims by the makers other than fast charging and non-spillable etc..
I was going to switch my own boat over to them last season, still ahve the new alt and regulator on my bench, but decided against it as the math just does not seem to add up in the real world. Besides my buddy Dave has talked me clean out if it by showing me under five year old AGM's that are dead on pallets every time I walk in the shop.
Wet's require maintenance but it takes me all of five minutes a couple times a year with some distilled water. I pay $144.00 for 225 Ah's with 6V wets and would pay about $588.00 for 220 Ah's with two 6V Lifeline's.
I could buy FOUR banks of wets, 4 X $144.00 = $576.00 for less than the price of one bank of Lifeline's. For those prices they should last twenty years minimum. Perhaps some have lasted 7-10 years but neither myself nor my friend Dave, who has been distributing AGM's for years, has seen it regularly.
My cost in Maine:
6V Wet Cells/225 Ah = $0.64 per Ah
6V Lifeline's/220 Ah = $2.67 per Ah
Don't get me wrong I like AGM's, and the technology, and they DO have their merits, but the manufacturers longevity claims have not stood up in the real world IMHO and with access to a distributor I can see and confirm this on a regular basis.
If you want to argue the merits of AGM's, and there are many, it is best to leave any sort of cost calculation out of it. We all know even the poorest treated 6V batts will last four to five years. Four banks of those @ 5 years life is 20 years. When AGM's start lasting 20 years, which would be $ for $ Ah for Ah, maybe then we can draw a cost comparison.
As Bill said above AGM's and lightly built alternators are a bad recipe and the alt will not usually last very long running at near full output. I have seen this on multiple occasions.
Get yourself a set of the Johnson Controls "Energizer" brand GC2 6V batts at Sam's Club. They run between $68.00 and $76.00 depending upon the club. I have a few friends going on 7 years with these as I type.. For those prices even if they last four years your still ahead of the game..