Re: Basic marine deep cycle battery questions
1. How 'big' (ie amphour rating) is the battery? What does your anchor light draw? LED?
2. Again, how big a battery and how many amps can your 'alternator' put out?
3. Xantrex and Victron both make good battery monitors that will do that for you.
Obviously the bigger the 'tank' the longer it will last, but it will also take longer to 'fill up'. Generally you should not run batteries down beyond 50% of their capacity in amps.. eg if you have a 120 A battery, you shouldn't use more than 60 before recharging it some. Typical outboard alternators are marginal outputs. A small solar panel may well keep up with your needs, esp in summer. Getting LED lights, esp for the masthead, will vastly improve your times between charges.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)