"BruceM" wrote in message
...
Guess it depends on your situation & how deep your pockets are.
Mine aren't very deep so I tend to always replace the start one each year &
put the original one in place for anchor accessory use (if you know what I
mean?).

If you replace a battery every year, you must have deep pockets! On my previous boat
I replaced all the batteries once in 8 years, and they had a number of years on them
when I bought it. On my new boat the house bank is going strong after five years. I
replaced the starter batteries with Optima's because they were stashed in a location
impossible to properly maintain - I expect them to go a number of years. A cheap
battery goes 4 years in a car ... why shouldn't a quality battery do the same in a
boat?

Usually by then that one is just about had it from too many low
drains. (Sharking at night with lights on & music playing & mobile phone
plugged in & depth/fish sounder on etc,)

If you look at the "discharge depth/service life" curves maybe you would size your
batteries appropriately. A deep cycle battery should be good for hundreds of cycles
as long as you don't drain it too far. A starting battery will only give you a
handful of deep cycles.

Perhaps I don't appreciate your situation (do you have to carry a recharged battery to
a moored boat?) but it seems like something is wrong if you're only getting one year
of good service from a battery!