AGM batteries - are they better?

msiminoff wrote:
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.

Thank you Mark. That's very interesting. My data (chart on previous page) was also collected from the serial output of a TriMetric, and the charger was a PD9280, not TC or PF corrected. I was charging 460AH FLA, as compared to your 300AH AGM. It's hard to get accurate comparisons, but the numbers I came up with showed very similar results for the time between 75A to 10A comparing my 80A charger to your 100A charger. I chose the 75A level, as that's about where the internal resistance/ battery cable resistance is dominating the charge rate - it's in the region where charge rate is falling rapidly. Even though I'm charging a 460AH FLA bank and you're charging a 300AH AGM bank, the time for the charge rate to drop from 75A to 10A is about the same for both of us (I measured 1.2 hours +/- .1 hours on both your chart and my chart). I would have expected much better performance on the AGM, first because the bank size of 300AH is less than my bank of 460AH and second because the internal resistance of the AGMs should be lower. Perhaps your charge cables are not as optimized as mine, which would affect that region. I'm using 1/0 copper, 3' in length.

Again, I'm not trying to convince anyone else that AGMs are worse, or not worth the money. I'm trying to figure out where it makes sense for me to spend money, and the more I look, the more convinced I am that I should focus on solar to finish off the absorption stage slowly, instead of trying to speed up my gen charging in that region. I just don't spend enough time in bulk mode charging for the higher charge rate that you get there to be an advantage for me.

Thanks a lot for that post!