T&T: AGM Batteries

[Richard Cook]

If I understand correctly, AGM batteries accept a higher rate of charge 
(amps) at the same voltage, because of their lower internal resistance. 
  Thus during the bulk charge stage, if the charging system is able to 
put out higher amps, they charge faster.

Richard Cook
New Moon (Bounty 257)



Jake2124 at aol.com wrote:
> 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