Good post Centaur agree with all that really, except with care flooded batteries last /that/ bad if not allowed to go too deep.
Capn, The bulk charge of a battery is the first part of charging and accounts for about 80% of its capacity. Assuming you have a terminal voltage of 12v or under the battery is 100% dead. So 80% of 110 is 88amps. Assuming again that your battery charger is capable of maintaining 6 amps continuous during bulk charge that it will take around 14 hours to reach this point and about the same again/ish to charge to the final 20%.
If its a fairly basic charger (Halfords or something) then chances are if its rated at 6A it won't/can't maintain this.
As for battery size. You can use anything you want, will just take longer to charge. If you have 80, changing to 90, 110 or even 200 would be fine, but charge times would be a bit longer obviously. You can sometimes get problems if you go too small however, but that will never happen on a boat. The only other problem is perhaps if you have a really old unregulated charging system like my old Fletcher had, voltage can go too high and you just waste it as heat in the battery and again can shorten its life (hence why I had the nav lights on, during the IOW trip)
All alternator outputs are about 14.4 volts. Some alternators have external voltage sensing - Toyota used this a lot. Nissan don't seem to. (at lest for the stuff I work on) I quite like this as it takes the battery terminal voltage rather than the alternator output voltage, so can account for losses in the charging cables etc.
In any case things that kill a lead acid battery are - in order of what I consider most serious first (others may have other opinions on this):Deep discharges
- Greater than 60-80% For ANY period of time - this will be the cause of why some people get -2-3 years and others get 4-6 years from a battery, the ones who get 6 years may have medium discharges but not deep, and then left like that for months. I expect most boat batteries die due to this, leads to rapid decline.Medium discharges
- long periods of time (weeks/months or more), say you never fully charge the battery and the boat is never used enough to fully charge it. Battery may have enough cranking power but won't last that many years.Never achieving full charge
- plates will suffer with sulphation as above^Lack of equalisation
- Its necessary to equalise a battery occasionally. This is carried out by a controlled over charge. I suspect many people would find their batteries last much longer if they did this. I'd say this should be carried about at least twice a year on a boat battery, or any used for 'Leisure' applications. I suspect in reality this rarely if ever happens.
And finallyFrequent over charging
- Batteries just don't like this - say broken alternator. Can dry the cells out leading to premature battery death.
I could write about this stuff for hours!!!