Absorption Charge

An absorption charge is the second stage of lead-acid charging, where the charger holds the voltage steady and the current tapers as the battery saturates. Battery University calls it the topping charge.

Battery University says this stage fills the last 30% of a lead-acid battery over another 7 to 10 hours. Skipping it regularly leads to sulfation and lost capacity. It also says a battery should not dwell at the topping voltage for more than 48 hours before dropping to a float charge.

This is why a 100 Ah battery on a 10 amp charger takes longer than the simple 11 hours 7 minutes estimate. The guide on how long to charge a car battery explains each stage.