Battery type is very important in how one maintains their batteries. Dry batteries (AGM) do not charge and are not charged the same way as wet (lead acid) batteries. Are you employing a 3 stage charge controller for your solar panels
? Do you keep load on the system? Is your alternator
a twin post or single
? Are your batteries 6VDC, 12VDC and in what manner are they wired? Every battery manufacturer has different settings for charging
and your charger(s) must be set accordingly dependent upon your battery setup.
It's easy to find the chart for the scale of charge a battery can take. Three month old batteries might only hold a true charge of 90% of their advertised amp/hours. (Nothing to do with voltage but the true indication of battery charge.)
Leaving solar panels
unattended (trickling) without going through a charge controller is unconscionable. At minimal it will create stray electricity through your grounding system (to the annoyance of others in your marina), cause battery run away or worse.
Lead acid batteries give the most amp/hours for the buck but take extra care with the maintenance
of adding distilled water
once a month. Your battery system (if monitored) may drop as low as 10 VDC but it's important to understand how many amp/hours are remaining NOT the voltage. I like to have a separate starting battery on it's own charging system. There's a number of ways to do this; ours is done with a twin post Balmar
with one side going to the "house" the other the "start".
Keeping your batteries in good health
may entail ever evolving technological changes but remember it's a science, not an art.