The 'green lights' are a waste of space. I've had batteries that were showing green and would barely put lights on the dash in a vehicle, never mind turn it over, and the one in my Discovery has been black (=replace) for about 5 years and is still OK. It's just over 12 years old (original vehicle battery) and still going strong, think that is the record for me.
If a battery has been very flat, you tend to find that an alternator will not bring it back up properly - it will work but it is better to trickle charge slowly with a decent charger.
A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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