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ContinuousWave: Small Boat Electrical
Life expectancy of a AGM (gell cell) vs. a lead acid battery
|Author||Topic: Life expectancy of a AGM (gell cell) vs. a lead acid battery|
posted 06-07-2009 02:39 PM ET (US)
My reason for this post is that after having a few lead acid batterys that only lasted 2-3 years, the AGM battery I had prior to going to a two battery set up which has been serving as a back up battery, and is going on 10 years old is still good. Does this say the technology, reliability and life expectancy of a modern AGM battery out weigh the cost difference of a lead acid battery?
posted 06-07-2009 03:14 PM ET (US)
An AGM battery is a lead-acid battery.
posted 06-09-2009 09:41 AM ET (US)
An AGM battery is not a "gell cell" battery.
posted 06-10-2009 04:02 PM ET (US)
The useful life of a lead-acid battery is influenced by the nature of its use and how it has been charged and maintained. The number of charge-discharge cycles, the depth of the discharge, and the nature of the charging all influence the battery's ability to store and deliver electrical energy.
posted 06-10-2009 06:02 PM ET (US)
Battery quality is generally related to battery price. Often comparisons are made between the lowest cost automotive battery that sells for about $40 and a premium AGM battery that sells for $250, or six times more expensive. This is something like comparing a vehicle that costs $20,000 with one that costs $120,000. Of course the quality of the product that costs six times more might be better. However, if one compares an AGM battery to a flooded cell lead-acid battery of comparable cost and quality, the quality and life expectancy of the flooded cell battery will be equal or better.
The SURRETTE company has been making quality flooded cell lead acid batteries for marine use for decades. SURRETTE offer an 84-month (seven-year) replacement warranty. In contrast, many AGM batteries are sold with only a one-year warranty. Not long ago there was an AGM battery which was very prominently promoted and mentioned over and over in internet discussions by promotors of this battery as a highly recommended battery, yet that AGM battery had only a one-year warranty. As a general rule, I do not find it reasonable to think that a battery whose manufacturer supports it under warranty for one year is going to last longer than a battery whose manufacturer supports it under warranty for seven years.
In my opinion one reason for the surge in popularity for AGM batteries is their ability to be shipped in a fully charged state without risk of acid spill. This has permitted the manufacture of AGM batteries to move to the Far East where they can be made at reduced cost and then shipped to overseas markets in a ready-to-use condition. Flooded cell batteries require more careful shipment and must be filled with electrolyte and charged at a distribution center or by the retailer.
While it is possible to find operational advantages to the AGM battery compared to a flooded cell battery, such as in the case of military vehicles which are subject to hostile gunfire, I do not think that long life span is an inherent advantage, and, if consideration is given to the limitations of the AGM design, it is more reasonable to presume a flooded cell battery will last longer. Flooded cell batteries in stationary power applications often last for decades when carefully maintained.
posted 06-11-2009 06:13 PM ET (US)
An AGM battery can be fabricated with less susceptibility to shock and vibration vs a flooded cell battery. Comparison to a fixed location on shore is not really a fair comparison to the marine environment.
Other advantages that favor an AGM battery are that they do not require charging for extended periods, they do not out-gas hydrogen under normal conditions, they cannot spill electrolyte and you do not need access to them to check and top off the electrolyte level. Even if the life were the same, these advantages are significant.
posted 06-11-2009 09:51 PM ET (US)
If we want to change the topic away from the life expectancy, it is possible to make all kinds of arguments in favor or against the AGM battery, but I think it is best to stick to the topic. The initial proposition was that an AGM battery lasts five times longer than a conventional flooded cell lead-acid battery. I think that is bunk. As I mentioned, it is not unusual for a flooded cell battery to have seven times longer warranty than an AGM. Why on earth would a manufacturer provide a warranty that was seven times longer on a battery that was only going to last one-fifth as long as a battery with only a one-year warranty? If you do believe these claims and do the math, the conventional battery should only have a warranty for 12/5-year or 2 months and 12 days. Yet a flooded cell battery of comparable price has a warranty for seven years. This does not make sense. Someone is deluding themselves.
As I have mentioned previously, at work I have $20,000 worth of AGM batteries in service (80 jars at $250 each) and we can barely get four years of useful life from them.
posted 06-12-2009 07:13 AM ET (US)
I guess a way to summarize would be to say the life expectancy of an AGM vs. a flooded battery depends on the intended usage. But, as pointed out, there are much more important considerations other than battery life span when considered for marine use.
posted 06-12-2009 09:54 AM ET (US)
Just to make clear, when we complained to our vendor about poor battery life from the AGM cells, his recommendation was to change to flooded cells.
I appreciate that AGM batteries have become popular, but I do not believe that they last longer than flooded cell batteries. I do not accept the initial premise that an AGM battery lasts five times longer than a flooded cell battery.
I do not dispute that the AGM battery has other features. It is great in jet fighter aircraft where it works during inverted flight and a flooded cell could not.
posted 06-12-2009 07:10 PM ET (US)
Since you referenced it two times, what the he'll do you do with all those batteries? (for work that is)
If I am off topic, just delete.
posted 06-12-2009 08:32 PM ET (US)
Re the 80 AGM batteries: The AGM batteries are connected in series, 40 of them, to generate about (40 x 13.2) 528-volts DC. This voltage is used to create an alternating current for a Uninterrupted Power Supply (UPS) on a three-phase 208-Volt feed. There is about 1-ampere of floating charge current on the string. The UPS jumps on to take the load whenever the input voltage falls below threshold. All cells are individually monitored for voltage and internal resistance. The general failure trend is for the internal resistance to grow. Because of the series connection, any cell with high internal resistance is a problem and must be replaced. The UPS is designed to sustain power at high load (about 70-amperes) for about ten minutes while a generator starts and comes on line, and also to instantaneously come on-line for short periods when the input voltage suddenly varies or dips.
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