I second Mike's recommendation that you review West Marine's discussion about batteries. It's in the West Advisor (under the Advice & Articles tab, look under "Electrical" and then the article titled "Selecting a Marine Storage Battery." URL here: http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorView?langId=-1&storeId=11151&catalogId=10001&page=Selecting-a-Marine-Storage-Battery I don't know from your post exactly what you need - you said you need to replace your starting batteries. What you don't say is whether you have a separate deep-cycle battery bank for house use when your engines are off and you're not hooked up to shore power (lights, refrigeration, etc.) If you do, then for your starting bank all you need is a standard automotive-style starting battery, the kind you can get at Costco, Sam's Club or Sears. These batteries are designed to deliver a short burst of high power. You'll kill them if you run them down, like using them for house loads over a weekend at anchor. They're not built for deep discharges. You don't need a "marine" battery for pure starting loads. If you have a separate bank that you use only for house loads, you need dedicated deep-cycle batteries. These are designed to be drawn down substantially and recharged repeatedly - which is treatment that will kill an automotive (e.g., starting) battery. Best price around Seattle that I've found on these is the Dyno brand at Fisheries. If you use your batteries for both starting and house loads, then you need a dual-purpose battery, like the "marine" battery at Costco or other discounters. West Marine sells dual-purpose batteries, too. So does Fisheries Supply - and they might be more competitive than West. On the battery chemistry debate, I weigh in heavily on the side of old-school flooded batteries. Yes, AGM and gel-cel batteries are great and don't leak (although they do outgas and need to be vented like flooded batteries), but the cost difference is (to me) not worth their added benefits. The only benefit I can see that I would like about AGM batteries is that they will accept a higher rate of charge acceptance (which translates to shorter charging - e.g., engine-running - times). A flooded deep cycle battery will accept a charge of approximately 25% of the amp-hour rating versus the AGM charge acceptance of about 40% - but this doesn't matter to me because I have a house bank of 2 8D batteries, which have an amp-hour rating of 255 each (510 both). This means that my flooded batteries will accept up to 127.5 amps of charge versus an AGM acceptance of 204 amps. I have a 40-amp fixed AC charger and 60-amp alternators on my twin engines - meaning that I can't charge my flooded batteries as fast as they will accept a charge. Having AGM batteries would be even more underkill as far as my charging system goes, so I wouldn't save any charging time. Price comparison: 8D flooded deep-cycle batteries at Fisheries Supply: $374.49. 8D AGM batteries at Fisheries Supply: $814.36. I can't justify more than 2x the price for the no-spill convenience. Plus, flooded batteries will tolerate overcharging better than AGM or gel-cells will. My advice is worth what you paid for it :^)
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