T&T: AGM Batteries

[Jake2124 at aol.com]

Some of the information regarding AGM batteries leaves me puzzled. Maybe 
someone can clarify. 

I understand that the maximum rate of charge for a deep cycle wet cell 
battery should be kept to about 25% of the capacity. So, a 100 AH battery should not 
see more than 25 amps. I also understand that AGM's can withstand a charge 
rate equal to their AH capacity, or "1C". So, a 100 AH AGM could be charged at 
100 amps. This is controlled by the maximum capacity of the charger, or by a 
maximum amperage setting on the bigger, more sophisticated chargers. OK so here 
is what is unclear. I keep hearing that you can charge the AGM in 1/4 if the 
time. I question that. Within a tenth of a volt or two, the charger will limit 
itself to around 14.5 V. So, while you may not have to limit the charge rate 
on a dead AGM, won't the battery resistance increase quickly and limit the 
current inflow just like any other battery? Are you saying to use what ever 
voltage it takes to charge the 100 amp battery at 100 amps till fully charged? I 
don't think so. I can see that a really discharged AGM will charge faster than a 
wet cell without damage, but probably not even near 4X faster overall. Also, 
if you push the AGM to the full 1C charging rate, is that really the optimum 
charge condition for long battery life?

Brian


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