I am looking into changing my 2 deep cycle batteries that keep failing on me.
any suggestions for a good battery, inboard charger setup for a 27ft sailboat that doesn't use to much power normally for 2-3 day trips. Always docked at marina with power when not in use
If your batteries are 'failing on you' they are probably 'done'. If you're not running a fridge, and esp if you're not running a lot of lights, or you're onto LEDs already then your usage is going to be very low indeed. Your needs won't be extreme.
If you were to get a good 100-120A/h deep cycle battery that should do you for the three and four day trips if you leave fully charged. Most outboard alternator's are weak and ineffective, but a modest solar panel would likely keep you going in summer. A pair of 6 volts wired in series would do you nicely too if you have the space for them.
Do a power budget so you have an idea of your actual usage. One of the problems with building up a large storage bank is that, though you can go some time without charging, if you run them down eventually it takes a very long time to bring them back if you don't have an effective charging system. I suppose nowadays if you've got kids and you've all got to charge up all the devices (phones, ipads, DVDplayers, etc etc) that your usage could be higher than one might think. For example a laptop on a small inverter can use as much power as a large fridge.
I'd keep a dedicated starting battery if your engine is electric start, otherwise no worries.