How long does it take to charge a 100Ah battery?

About 11 hours 7 minutes from empty on a 10 amp charger for lead acid, before the slow topping stage. At 90% efficiency the battery needs 111.1 Ah. A lithium 100 Ah battery is above 99% efficient, so on a 20 amp charger it needs roughly 5 hours.

The formula is the same for both: amp-hours needed divided by efficiency, then divided by charger amps. Lithium charges faster because it accepts more current and wastes less. Battery University puts a full lithium-ion charge at about 2 to 3 hours at 0.5C to 1C, while lead acid takes 12 to 16 hours.

Run your own numbers in the battery charging time calculator, which has a battery type setting. The guide to lithium vs lead-acid charging compares charge stages and current limits.