The dirty-little-secret about FLA Batteries

[davidbrady]

Foks,

There's a characteristic of all battery technologies quantified in the Peukert Constant which says that the shorter the time that you discharge a battery the less the 'effective' AH capacity of the battery.

Brand new batteries display this behavior but it only gets worse with the age of the battery and it's especially bad with Flooded Lead Acid (FLA) batteries. This is the dirty little secret about FLA's that no one talks about and this is where AGM's routinely outperform FLA's in the real world.

Here's a chart showing the effective capacity of a battery with different Peukert Constants:



Lifeline AGM's have a constant of 1.12; your typical FLA is in the range of 1.3 to 1.5. For instance, say your powering you 600W hair dryer, that's about a 50 amp draw from your 12V system. Looking at the chart, the AGM is performing at 78 AH while the best equally rated flooded/wet battery is only performing at a 38 AH capacity.

IOW's start your coach and you've dramatically cut down the available AH capacity of your battery. Start your coach with an FLA (flooded/wet) battery and you've effectively halved the capacity that you would have if you were running AGM's.

Folks, the battery company's published ampere-hour rating isn't the full story. You can't do simple math and truly compare AGM capacities with FLA (flooded wet lead acid) battery capacities.

So we know that:
1) the true (Peukert Constant) corrected real world AH capacity of AGM's outshines that of even the best equally rated wet battery,

2) in the bulk charge stage Lifeline's can be charged at 5C! That means a 100AH battery can accept a bulk inrush current of 500A. This is an impossibility with a wet battery and dramatically reduces AGM charge times, and

3) AGM's are happy with charge voltage up to even 15V. Many of us WB and LXi owners have been charging banks of AGM's with our 50DN alternators for years with little discernible ill effects.

AGM's are simply more robust and higher performing than Flooded Lead Acid batteries.