#1:Question: What's the best way to go in a boat, AGM (absorbed glass mat), Wet lead acid, or gelled electrolyte (gell cell) for my "house" (accessory, or non-starting) batteries on board my boat

Answer: The choice is yours depending on your view of value:

We sell AGM and wet lead acid batteries in all of the sizes: 24, 27, 30H (or 29H), 4D, 8D and Golf Cart sizes.

We also have some odd sizes too, such as 2volt cells, and the N-series for the Taiwan-built batteries and their respective boxes. Most big boaters (over 25') already have the 8D or Golf Cart batteries in parallel or series for their house batteries. Here is a rambling of Pro's and Con's for each of the three types.

AGM Pro's: better cycling and depth of dischager over the wet or gell batteries. While most wet batteries are supposed to only go to about 50% depth of discharge, the AGM's are able to go to about 20% depth of discharge without harming them PROVIDED that you don't overcharge them at too high a voltage on their return. What does this mean in numbers? If you have a Golf Cart battery that is 220 amp/hours for both the wet and the AGM, then the AGM would be able to have 176 ah. of useful capacity (220 X .80) vs. the wet battery at 110 amp/hours.

When comparing price for value's sake, if the GPL-4C costs $205.29 for 176 ah, that is a value of $1.16/ah. vs the wet battery at $69.20/110ah. with a value of $.623/ah. (54%). So why would a person buy an AGM? Read on.

AGM's need no watering and will receive a charge faster than wet batteries or Gell batteries. How much faster?

Concorde, our manufacturer of the Lifeline series, says over twice as fast. Throw Peukert's law out the window: the physical compression of the plates in the cell compartment, when coupled with the better quality of materials in an AGM give it far less internal resistance than the other types. Practically speaking this means less time to recharge your batteries while underway.

AGM's can be mounted in any position, require no room for venting and therefore can be installed in living quarter sections of your boat. This can be especially important if you already have a cramped space in mind for your batteries. Under the bunk, in the lazarette, under the molded seating area, or way up in the dark part of your boat are just fine for the AGM's. Also, because of the low internal resistance of the batteries, they were tested by the Coast Guard for their potential for explosion and they passed with flying colors (excuse the pun) by not exploding when heated to 200 degrees f., then dead shorted! So these are some amazing batteries.

AGM's also are virtually maintenance free: although everyone should visually check the terminals and general condition (for swelling, corrosion, black post, or high temperature) of a battery at least every six months, or before a big trip. The charts that Lifeline has also state that they have more life cycles than Gell Cell batteries (insert chart). Will they last longer than the wet lead acid batteries? Who knows: we have an old addage in the battery stores that states that "batteries don't die, their owners kill them."

AGM Con's: Price is pretty stiff when compared with the wet lead acid batteries--generally by 2 or 3 times. This difference begins to fade if any of the above items listed are important to you: cramped space, no maintenance, difficult mounting, rapid recharge, explosion-proof and non-gassing. But if you are from Missouri, the Show-Me state, and if you don't need any of the fancy features, and you are willing to slosh a little water or acid on your jeans from time to time, then the wet lead acid battery is a tough design to beat overall. As a value of Dollars per Amp/hour or Dollars per year life expectancy, the AGM takes a back seat to the wet lead acid battery if you don't need any bells and whistles.

Gell Cell (or gelled electrolyte where the acid is suspended in silica) Pro's: According to some of the folks who really need a higher number of shallow cycles, the gell cells do better. This contradicts the Lifeline chart but the folks who use the Kangaroo Kaddy and some wheel chair folks claim that the gell cells last for a longer period of time. At our stores, we have seen both AGM and Gell Cells poop out with too much cycling. I think that the jury is still out on this "Pro." This isn't much of a "Pro" is it?

Gell Cells were the first and some of the original Prevailer batteries from Sonnenschein are still out there. Exide has bought the brand and the technology from the Germans and is selling them today. We currently do not sell Gell Cells or any other gelled electrolyte batteries where the acid is suspended in silica. Read on for more Con's.

Gell Cell Con's: Price and a convincing argument that they hold up better and longer than the AGM batteries.

Although they were the first, they are not very popular at all any more. Perhaps this is yesterday's technology that has moved on.

Gell Cells do not do well in high heat locations (over 80 degrees f.) because of the voids that develop as the gelled acid hardens with cycling. As it hardens and dries, the capacity diminishes and the battery begins to swell as if ready to hatch. The voids that develop as the hardened acid pulls away from the plates is another reason for lost capacity. Eventually, the silica suspended acid pulls away from the plate and is no longer useful in the charging or discharging process.

Wet Lead Acid Pro's: Price and reliability. The wet lead acid battery is still the standard by which all other types are measured: dollars per cold cranking amp (CCA), per ampere hour (a.h.), or per year. If you are considering an 8D-AGM vs. an 8D-1550HDP (wet, heavy duty dual purpose), then the wet battery is easier to justify to your spouse for several reasons, most of which boil down to the words GOOD VALUE. A wet battery will last just as long as an AGM (assuming that you don't kill either one with over or under charging), so the dollars per year argument is out. A wet battery generally has a higher overall ampere hour rating than its pedigreed cousin, and the wet battery is more hands on for those folks who just feel the need to look inside the battery at the plates every now and again because it's "the right thing to do." You also can use a hydometer on a wet battery. The hydrometer is still one (of several) very reliable means of testing a battery's state of charge other than voltage (which can just be a surface charge).

Wet Lead Acid Battery Con's: Slower to recharge than AGM, require maintenance more often, and don't cycle as deeply as the AGM batteries. Let's start with the rechargability of the wet: again, we go back to the Peukert's law thing about resistance: the more juice you try to put into or take out of a wet battery, the more resistance you will experience. With an AGM battery, the literature would have you believing that it is a secret sauce that is in the AGM's that they omit in the wet batteries. Not so. A couple of years ago, I read a couple of abstracts and articles in Battery Man magazine (yes, I know, it's a sexist title, but it is the ONLY credible battery trade magazine since January, 1921) about how the recharge rate of AGM batteries is better because the elements in each cell are physically pressed into the cell compartment with a good deal of physical pressure. For some reason, this creates a better condition for charging and discharging the AGM batteries than having the element "dangle" in the cell with less pressure on each of the plates. The wet cells need to have space and volume around them to allow the flow, cool and allow transfer of ions and acid back and forth in the liquid solution. You may need to grant me a little poetic license here, my formal training is from a B.A. degree in History, not chemistry. In the AGM battery, compaction is better because the electrolyte is absorbed in the fibre glass mat which is sandwiched between the positive and negative plates, rather than freely floating in the cell. The tight compaction of the element in the cell allows the dense mat to have immediate contact with the positive and negative plates. If the elements' potential for transmission of electricity is under physical pressure, then the ability for electricity to flow is better. Better flow of electricity (or voltage acceptance potential) allows us to charge the battery faster. Whew. How about that for a theory? Hey, it's better than the "secret sauce" theory that most brochures pontificate.

The other Con of the Wet Lead Acid battery: Maintenance. Yep, this is the part where, no matter how good you are at staying neat, you will always end up with acid holes in your best jeans or boating chinos because you are using a hydrometer. The acid drops and smears are indistinguishable from water. By the time you think about where you parked your bottom, near the batteries, you are in the acid clear through to your underwear. You won't know it until you wash your clothes. So don't forget to add couple of pair of pants and a shirt or two to the price of your Wet Lead Acid batteries. AGM batteries don't generally leak acid unless overcharged or broken.

The Last Con of the Wet Lead Acid battery: Depth of discharge is generally thought to allow you to discharge the battery down to 20% of its rated capacity (see description of value in paragraph 3).

So if you are still trying to justify the disadvantage of a Wet Lead Acid battery vs. the AGM,

consider that the decreased USEFUL capacity of a wet battery inhibits your enjoyment by roughly 30% for the same number of batteries. AHA! That's really something if you have a very limited space aboard your boat. If the AGM cost 100% more than a wet battery, then we need to come up with at least 71% more reason in order to justify the purchase:

add 20% you'll have something "cooler" than a regular battery: you will have the latest, greatest battery with a pedigree.

add 20% for no hassle of standing on your head to fill 'em with distilled water, sitting in or flicking acid on yourself.

add 20% for the added USEFUL ampere hour capacity without having to stow, secure and connect (wire) another battery to increase your "off the dock" time.

add 15% for faster recharge time, less engine or generator run time, safety from explosion, and more storage options.


There! You are over the top for reasons to buy the AGM batteries: they are at least a 4% better value than the Wet Lead Acid batteries.

Question #2: What about Marine Battery Chargers? I will divide this into a couple of commonly asked questions:

2A: Do I need a new or different charger for AGM batteries or Gell Cells or Wet Lead Acid batteries?

2B: Can I just use the charger that is built in on my inverter to handle my starting and "house" batteries?

2C: Do I need a constant voltage/variable amperage charger?

Let's take #2A: Do I need a new or different charger for AGM batteries or Gell Cells or Wet Lead Acid batteries?

Generally no, but maybe in your case. It all depends on if your charger is settable.

We sell Lifeline batteries as our proven AGM batteries for cycling and have quite a few choices in the 8D.

We sell a real whopper of a dual purpose 8D made by Douglas Battery of NC, that has 1550 CCA, and 510 minutes reserve capacity. Now here is the big question for you: are you buying batteries to meet charger's settings or are you buying them to meet your actual needs for house vs. starting?

I am a little suspicious of your Original Equipment (OE) charger/converter. The answer to whether or not your charger "fits" your batteries or not lies in the output voltage of that charger. The charger industry has many different opinions about the charging characteristics of AGM vs. Gel vs. wet batteries.

Here is my opinion: AGM batteries do not and should not receive an "equalize" charge: it's too high and hot for the batteries and, beside, there is no stratified electrolyte that needs to be equalized or mixed in AGM batteries anyway. Equalizing the AGM batteries only will shorten the batteries' lifespan. Float voltage should be set at 2.25 volts/per cell or slightly less. This will give you a float voltage of 13.5. 13.4-13.5 volts is recommended by Concorde, the maker of Lifeline batteries (America's most popular AGM marine battery).

Wet batteries should float at about 13.2 volts. If you do more, then the batteries will gas and need more watering. Higher float voltage also tends to prematurely galvanize and corrode the plates--shortening the life.

That being said, you will need to have a charger that will periodically (either automatically or manually when you visit the boat) equalize the batteries. Equalizing isn't rocket science: it stirs up the electrolyte by bubbling it. This also causes that dreaded sulfation to get knocked off the pasted plates. Setting the bulk and float voltage is then needed. Set the bulk voltage according to the output voltage of your alternator(s). If you have no setting or control over your charger's voltage, you have two choices:

A) throw away that "perfectly useful" and shiny charger (often tough to convince the spouse) and continue to buy more batteries more often. OR B) buy a 3 or 4 step charger specifically for your starting battery bank.

Good ones cost about $200. to $350 such as the Guest brand that we sell in our stores. They are marine rated, trustworthy and will treat your batteries (whatever type you decide to buy) with the respect that they need.

#2C IF so, would the stock charger damage agm/gel batteries? Is the battery charger in the inverter enough capacity to take care of all the batteries?

Yes the inverter has a good charger function, but usually is not set up for 2 or more banks (like you have: starting and "house"). Also, depending on whether you are a live-aboard or not, you may want a little more of a constant voltage, variable amperage charger. A McCarron charger would do the whole works. If you are not a live-aboard, then a Guest charger on the starting batteries is a good idea and let the inverter charge the house batteries whenever you are in port. The charger output is (or can be set) quite high and fast if you prefer for better recovery after living "on the hook" for a while and having run down your batteries. We sell Xantrex (formerly Trace and Heart inverters) and you should always keep the banks separate as much as possible so that you are not in danger of having no power to start your engines for the reason of too much camping.

Too sum up: we can help you with any battery or charger combination. If you need installation, then you will need a good electrician. If you are in the Everett area, I can make a couple of suggestions. If you are outside of the area, I won't be able to help you there.

I hope that this is some help to you. Please let me know if I can answer any more questions. You are welcome to call me at (800) 326-7406, outside the area or (425) 259-9260 locally.

Home Page | Contact Us | About Batteries | Returns/Warranty | Corporate Profile