Deep Cycle Battery Charging From Alternator

atp20 wrote:
Hello,
The 120A(?) alternator charges at 14.4 volts when the battery is full.

Is you alternator the only charging source?

Pretty much impossible to get from 80% charged to 100% charged in less than 3.5 hours. Ideally if you were to drive this 3.5 hours, the vehicle's voltage regulator would ideally be holding voltage in the 14.4v range and this would also be reaching distant house battery, over thick copper cable/circuit between alternator and house battery.

BUt your vehicle is extremely unlikely to hold 14.4v after 3.5 hours driving, meaning they are not recharging as fast as they could/should.

Do not check voltage once after engine starting and expect this is the voltage the vehicle's voltage regulator always allows.

Intermittent use....Put a solar panel on the roof, it will have the time to get them full and keep them full between intermittent uses, but get a solar controller with a battery temp sensor for South Florida summers.

Getting the AGMs full between intermittent use is paramount to longevity. If you fully charge them from the grid, and then fully disconnect them from all loads, they should not self discharge much at all. as low as 1.5% and as high as 5% per month, but higher in hotter ambient temps.

If the only charging source continues to be only the alternator in intermittent use, 2 years is all you can expect from any lead acid battery no matter how high its perceived or actual retail value.

Flooded deep cycle 6v jars might wake back up some from an extended equalization charge upto 16.2v after such abuse. But perhaps not.

How you get your batteries full is up to you, but if you want more than 2 years from them you have to gt them full regularly, and hopefuly promptly after any significant discharge