AGM batteries - are they better?

DryCamper11 wrote:
Does anyone have charge curves for AGM showing the performance (preferably with an 80A charger)? I'd particularly like to see the tail end of the charge cycle. How do AGMs perform? Is it significantly better than FLA batteries? Do AGMs taper the charge rate the way FLAs do, or is the entire advantage in the fact that I could run a bigger charger (100+ A) for my 460AH battery bank?

Here's a charge curve for my three Odyssey PC2150's (~300Ah total) from 50-100% SOC with a 100A (power factor corrected & temperature compensated) charger. This data was collected from the serial data output of my Trimetric.

Note that for the first ~90 minutes of the charge cycle I had (inadvertently) set the charge current limit to 35A... after that point I increased it to 200%C and the current jumped to 110A. As you can see the "curve" looks similar to what you would expect with FLA batteries except that the initial (bulk) charge acceptance is much higher, which means that time to 100% SOC is shorter.

I absolutely love my AGM's and for me they are indeed "better". However my usage is not typical... I despise running my generator (a Honda 2K). I do extended boondocking and never have hook-ups (unless parked in my driveway). I have enough solar so I can typically re-charge (~95-100%) daily I have programmed my chargers (solar & inverter/charger) to precisely follow my manufacturer's published spec', and have a 180A alternator that charges at 14.7V. I run high current devices (e.g. microwave) from my inverter for short periods of time, moderate loads (e.g. the A/C) for hours at a time. My batteries are installed in my (climate controlled) basement so they're not easily to access for maintenance, but this location provides optimal weight placement and allows for good cold weather performance.
I'll add that my starter batteries are also AGM's so they can be charged and/or discharged in parallel (same voltage).

Yes, the initial purchase price was high... Althought I haven't taken the time to do the calculation, I suspect that (in terms of the long term cost of ownership) my AGM's will net out at about the same dollars-per-kilowatt-hour used over their lifetime when compared with my previous 6V GC FLA batt's. Most importantly they deliver the type of performance I need for the style of camping I want to do.
AGM's are not "better" for everybody and for a lot of folks they're likely to be worse. If you can't charge them correctly, AGM's are definitely not worth it. Caveat emptor!!

Cheers,
-Mark