Once the battery is fully charged it will not accept any more energy (current) from the charger, since all the energy levels that were depleted when empty are now at their highest level.
Lead acid is sluggish and cannot be charged as quickly as other battery systems. (See BU-202: New Lead Acid Systems) With the CCCV method, lead acid batteries are charged in three stages, which are constant-current charge, topping charge and float charge.
So many lead acid batteries are 'murdered' because they are left connected (accidentally) to a power 'drain'. No matter the size, lead acid batteries are relatively slow to charge. It may take around 8 - 12 hours to fully charge a battery from fully depleted. It's not possible to just dump a lot of current into them and charge them quickly.
Does a lead acid battery change resistance compared to state of charge?
Below is a chart I found of the changing resistance of a lead acid battery compared to state of charge, however, the charge acceptance is higher when it is discharged compared to when it is charged. How does this happen with a higher resistance that gradually gets lower? I'm also assuming a constant charging voltage from an alternator.
The charge time is 12–16 hours and up to 36–48 hours for large stationary batteries. With higher charge currents and multi-stage charge methods, the charge time can be reduced to 8–10 hours; however, without full topping charge. Lead acid is sluggish and cannot be charged as quickly as other battery systems. (See BU-202: New Lead Acid Systems)
Lead acid batteries need a specific 3-stage charge process 6 in order to preserve their condition. In practice, if you don't discharge a battery beyond 50%, it takes less time to recharge the battery 7. It can be a good idea to hookup unused batteries permanently to a 'tricklecharger'.
The charging voltage should also be adjusted according to the battery's temperature, as higher temperatures require lower voltages to prevent overcharging. When it comes to charging a new lead acid battery, it is important to use the right charging current to ensure a longer lifespan and optimal performance.