The best charger is one that has mulitple charging rates and ends with a float charge like kb has. Anything else can overcharge and boil off the water if left unattended which will shorten the life, especially a sealed or agm battery. Batteries need to be maintained at full charge for a full life. A good solar panel is a great idea, not the cheap ones but a good one, read the volts they put out as the cheap ones put out only 12 volts which is not enough, the better ones put out up to 15 volts. Basically at 12 volts the battery is undercharged.
Battery 101
Batteries consist of lead dioxide (positive), sponge lead (negative) and sulfuric acid (electrolyte) arranged in a series of plates to form a cell of 2.1 volts. A twelve volt battery is made of 6 cells to give 12.6 volts. (stainless steel downrigger wire, zinc, saltwater make a battery of about .85 volts)
Under discharge the plates interact with the electrolyte to form lead sulfate and water. (thats how a bulb battery tester works, its measuring the density of the fluid, more water, less dense, less charge) The lead sulfate and water is returned to lead dioxide and sponge lead by charging the battery.
Here is the problem with not keeping the battery charged up. The lead sulfate after a few hours begins to harden and crystallize and this is difficult if not impossible after awhile to change back resulting in a loss of battery capacity. All batteries suffer this and this is what causes them to die although the life expentancy can be greatly extended if they are maintained.
Deep cell batteries stand up the best to this, they have fewer but thicker plates able to last longer but cant produce high current compared to similiar size starting batteries. Starting batteries have more but thinner plates in the cells allowing high current but the plates are very sensitive to deteriation from under charging. Deep cells are the best for marine application unless you need a high current for certain motors like my 200 optimax, it needs a lot of juice to fire up the electronics and compressers so I have a starting battery to start it and a deep cycle for the house wiring.
Also, what shortens a battery life is excessive vibration, a battery being knocked around or vibrating causes the lead sulphates to fall off the plates creating loss of capacity over time. Another maintance tip is to keep the top of battery cover clean, after awhile the top gets a layer of acid / gunk on it and this actually causes a circuit for current. Put a volt meter down on the plastic case besides both posts on a dirty battery and you will see about a volt passing over the top from post to post.
Im sure most of you know this but for those that don't, hope it helps.
cheers
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