I know you swear by these recommendations, but they are somewhat
conservative in my experience.

BTW, these comments relate more to alternator charging than shore power.
For those that are on the move, shore power chargers should be sized
to give a complete charge overnight, since there is little benefit to
"filling up" in less time. A 40 Amp charger is fine for most, assuming
it has the appropriate smarts to handle special cases like equalizing
and float. Weekend warriors can get by with smaller chargers, but
trickle chargers might leave the bank chronically undercharged, which is
bad.

more comments interspersed ...


Basic rules of battery life straight from an old time Trojan
application engineer who had forgotten more about wet cell batteries
than the rest of us will ever learn.

T105s are happy when kept between 60%-65% and 90%.

This is true, but they should be fully charged whenever possible.


For every AH hour you consume from a battery, you must replace it with
1.25AH.

The Charge Efficiency Rating that Trojan advertises for their wet cells
is 89%. I use 87% on my AH meter, and it generally proves to be too
conservative, that is, after several days on the hook my batteries are
more charged than the meter says.

This is a complex issue, since high discharge rates will discharge the
battery faster, a thus make the CEF appear lower (Peukert's Law at
work). In practical terms, if the discharge rate is higher than 5% of
the capacity per hour (that is, if a 400 Ah bank uses more than 20 Amps)
you will notice this effect more. This is one advantage of the new DC
"constant cycle" or Danfoss fridges are over the traditional holding
plate systems. I often force my fridge (which draws up to 35 Amps) to
cycle while the engine or generator is running in order to avoid this issue.


A bank accepts recharge at an average of 15% of the AH capacity yes
the instantaneous can exceed 15%.

I have used a "smart regulator" for the 16 years on two boats. In both
cases the charge rate started at 25% and did the bulk of the charging at
around 20%. When it drops below 15%, I figure its diminishing returns
and stop charging.

Of course, this only gets then up to about 80-85%, and if you require
going to 90 or 95%, that will require long charging at lower rates. My
solution is to equalize after a trip that involved many "incomplete
recharges" so as to remove any sulphation before it hardens.

In practice this means that my 4 T105's (450 Ah when new) are accepting
85 to 90 Amps for a considerable period. Its actually higher than this,
because the Ah meter (Xantrex Link 2000R) is factoring in the 87% CEF so
the Amps out of the alternator are somewhat higher.

This summer, the regulator started acting up, so I swapped in the old
stock alternator with a built in "dumb" regulator. It ran much closer
to the numbers Lew mentions. Fortunately we were in Maine, so the load
from the fridge was greatly reduced; had it been in the tropics this
would have been a real annoyance.


If you consume 100AH from your 400AH bank, you must replace it with
125AH at a 15% rate or about 60A which will require about 2 hours.

The above are the rules you live by with wet cells.

Unless of course you get an assist from modern technology and reduce the
charge time to about 90 minutes. I'm not quoting from books, I'm using
my real experience over the last 16 years. Our normal summer routine is
to spend a week or more at each anchorage, relying mostly on engine and
occasional genset time to recharge daily. The batteries have been
mostly Trojan T105's which have lasted about 6 years.

....


Want to increase the time between recharge cycles or reduce recharge
time, increase the size of the battery bank.

absolutely true

A bigger bank with accept a higher recharge rate.

In addition, it suffers less at high discharge rates and probably
overheats less.