Key phrase?:

Last summer
they seemed to loose their ability to keep my refrigerator and anchor
light working as long as they used to

Sounds like your bank is too small. You should try to avoid running the
batteries down more than 50%, (even deep cycle), to get the maximum life out of
them. If you are running off these batteries until the refrigerator and anchor
lights "aren't working" then you are likely discharging more of the capacity
than you should.

Calculate you amp load by adding up the amps consumed by all loads, and
multiplying each loads by the number of hours used in a day. Then multiply that
figure by the number of days you go between recahrges. Multiply the final
answer by four to determine how large a bank you should have. (The first "two"
enables you to avoid discharging beyond 50%, the second "two" accounts for the
fact that a battery reharges very quickly between 50 and about 80%, and then
much more slowly after that. Your "sweet spot" between the 50% minimum and the
80% easily attainable recharge is 30% of the battery's rated capacity. 30% x 4
= 120%, a reasonable reserve)

Two Group 27's should be OK for a night or so on a boat using just a moderate
amount of DC. (I usually shut off the refrigerator about bedtime and avoid
running the 5-amp load for 8 hours until morning, but that's just me.)

The other thing to check is your voltage regulator. Are you sending the
batteries to
hot a recharge, and consequently slowly destroying the internal plates?