posted 03-29-2011 09:00 AM ET (US)            

There are a couple of disadvantages to AGMs such as higher weight, initial cost, and some older or smaller outboard engines may lack the charging capacity needed to maintain AGM requirements.

Most who have been using AGMs for several years will, I believe, recommend them. I also believe the lifetime costs may be lower than with old technology batteries. Certainly the maintenance requirements are much less with AGMs. They never require water to top up the electrolyte and in my experience with them installed in a closed space they never need cleaning. They maintain a charge more effectively when not in use. I used AGMs in my previous Whaler for about eight years and they were going strong when I sold the boat. Other than a top off charge after long periods of non-use they received no maintenance.

We all have budgets we have to contend with but I found AGMs to be a little like GPS in that once you have the technology you won't want to be without it.

posted 03-29-2011 12:07 PM ET (US)            

Flooded cell batteries tend to outlast AGM batteries because the electrolyte can be refilled. All batteries where long life is important tend to be flooded cell batteries which can be refilled.

Most of the battery comparisons that tend to be made which favor AGM batteries over flooded cell batteries are between a $45 cheap flooded cell battery and a $295 AGM. If you compare batteries of similar cost and quality, the AGM and flooded cell batteries compare very favorably. Of course, if there is concern about a spill, the sealed battery wins that comparison. There is no debate there. But I would not try to promote AGM batteries on the basis of significantly lower self-discharge or on longer life, because those qualities are not recognized as being inherent in the AGM compared to flooded cell.

The AGM will have a lower self-discharge than other sealed batteries which are often called no-maintenance batteries because the lead in those non-AGM sealed batteries is often alloyed with other elements to provide more strength so that the plates can be made thinner. But in a good-ol' hulk and heavy-duty lead-acid flooded cell battery the plates are thick and made with lead of high purity. It is the lead purity which affects self-discharge rate, not the absorbed electrolyte.

For more on self-discharge of storage batteries, see these threads:

posted 03-29-2011 12:17 PM ET (US)            

The batteries are probably made in China by the cheapest possible supplier if they're AGM batteries. The sealed nature and lack of spilled acid in an AGM also allows them to be made in China and shipped to the USA for sale. Flooded cell batteries have to be shipped dry, then filled with acid, charged, and carefully delivered to retailers.

If the batteries are not AGM they're probably made in the USA by one of a handful of actual battery manufacturers.

High-volume retailers often are able to buy and sell commodity items like batteries at low prices because they negotiate good pricing from the manufacturer and keep their overhead low by avoiding advertising for the brand. The KIRKLAND brand demonstrates the lack of advertising by the fact that I have never heard of it before its mention here. I consider myself to be well acquainted with battery brands, so to fly under the radar as it has the KIRKLAND brand must be rather obscure.

Since it is a house brand of a specialty retail-club vendor, it hardly matters what the brand name might be. The manufacturer probably insists that their product not be sold under the recognized brand names usually associated with the manufacturer so as not to create a dispute with its other outlets selling the recognized brand at higher prices.

posted 03-29-2011 06:48 PM ET (US)            

Your points are taken. At least you didn't say flooded cell batteries require less maintenance and attention than AGM batteries.

Not having done testing of my own I can't argue that your tests concluding AGMs do not have a better self discharge rate than flooded cell batteries. However, my experience with low maintenance/sealed flooded cell batteries which are commonly sold as marine batteries by many outlets indicates the AGMs self discharge at a lower rate.

You seem to imply that AGMs are generally manufactured in China. Did I get that right? If so, perhaps you are correct but I've only owned Optima and DieHard AGMs. I believe Optima moved to Mexico or perhaps China(?) but I believe DieHard AGMs are manufactured in the US by Odessy (?sp) but do not know this to be a fact.

I can also report that the first pair of AGMs I installed lasted me for eight years and were in use when the boat was sold. I have never had a flooded cell battery last as long. Even when operating power plants which use large banks of flooded cell batteries to provide static excitation for voltage control I found battery life frequently less than eight years. The battery banks in power plants receive a lot of maintenance and attention due to the criticality of their function.

AGMs are not the best battery for everyone's boat, but they are the best for my boat and I therefore recommend them to others.

posted 03-29-2011 07:44 PM ET (US)            

The self-discharge rate of an AGM is mostly affected by the purity of the lead used to make it. It is not intrinsic that all AGM batteries will use high-purity lead. AGM refers to the technique of an absorbed electrolyte, not to high-purity lead. It is entirely possible for an AGM battery to use lead whose purity is no different than another battery. The only way an AGM battery has low self-discharge is if it has been made with high-purity lead. The better AGM batteries are made with high-purity lead, but then so are the better flooded cell batteries. So we are back to my point: an AGM battery cannot be said to always have a lower self-discharge rate than other batteries. It depends on the AGM and on the other battery.

Many--perhaps most--AGM batteries are made in China. Certain boutique-brand AGM batteries may be made in the USA. For replacement service in large uninterruptible power supply (UPS) devices, in the past four or five years, I have purchased 120 AGM batteries in three flights of 40-batteries. All were made in China. I asked our supplier if he could furnish AGM batteries made in the USA. He could not. He told me that the AGM batteries he could get were all made in China.

posted 03-29-2011 09:22 PM ET (US)            

The Sears Platinum Marine batteries are made by Odyssey Batteries:

posted 03-30-2011 09:02 AM ET (US)            

Jim, I assume you're using two volt one cell batteries in your UPS system. I can understand going to AGM batteries in that application. As you said maintenance and ventilation for sixty plus batteries and the interconnecting cables is quite a chore. The explosion hazzard is also significant and worries over damage and injury due to handling electrolyte are present. The charging system is another source of trouble as it ages.