Roger Long wrote:

Should I leave the charger on for some period of time regardless of what the
LED's are doing?

Giving a simple answer is not easy, Roger. But my answer is Yes, leave
the charger in float as long as possible.

Are you hoping to get maximum longevity from your AGM batteries? Or
just acceptable performance?

Unfortunately, experts disagree on exactly how to get maximum longevity
from AGMs when used with the use pattern you describe. The experts I
consulted for my Concorde AGMs said best practice would include:

· when possible, recharge every day the battery bank is used and as
soon as possible after use;
· when not in use, maintain the bank at 100% State of Charge by
continuous float charging;
· avoid Depths of Discharge approaching or greater than 80% of
amp-hour capacity;
· avoid recharging after shallow discharges of less than 10% of
capacity; and
· never discharge the bank to or below 11.8 volts.

If not keeping the bank on float when the boat is idle, the experts
advised me to leave the bank float until the charge drops below 1 A (my
bank has a nominal amp-hour capacity of 500 A-hr). That's a longer
float than one would specify for conventional wet lead-acid batts.

In addition:
· equalise the battery when the Charge Efficiency Factor falls below
90 or every three months.

AGMs have a lower shelf discharge than conventional wet lead-acid
batts, so you should not be surprised that your charger brings you bank
up to float quickly after a few months of non use. The first question
for you, given the above, is whether you should charge the battery bank
(ie too shallow a depth of discharge) after a few months of non use.
And question two for you is whether you should add a battery monitor
that delivers you information about the depth of discharge and the
current going into the battery.

As to when your particular charger transitions from acceptance to
float: check the specs. Some chargers impose a time limit on acceptance
for AGM and conventional wet lead-acid batts of 1 hour and 3 hrs for
gel batts. Other chargers have a predetermined point on the acceptance
curve (ie during the acceptance phase, the charger holds the voltage
across the bank constant - usually at or close to the bulk charge limit
- and slowly drops the current flowing into the bank. When the current
has dropped to a preset value (either preset by the manufacturer or by
you when you matched your charger to the amp-hour capacity of your
bank), the charger transitiions to float. That transition point is
usually 5 A, 10 A, 15 A - whichever is appropriate for your battery
bank or for what the manufacturer guesses is the likely capacity of
your battery bank. So question 3 for you is whether you should care
about the float LED or check the float charge instead and only turn off
the charger when it has dropped to a low value (eg 0.2 A, which is what
I'd guess might be appropriate for your battery bank).

All of the above is only relevant to occasional use of AGMs (as opposed
to constant use - most batts when used constantly live a lot longer
than those in occasional use). And much is contentious (ie I expect
someone to contradict what I've said).

Cheers

Bil