It's not exactly the same as your scenario since my battery is charged, but I decided to take some actual readings:

If you're starting with a weakened battery, the time required to get back to a charged condition will probably be longer, but my charging current dropped to pretty consistent 1.5A within a few minutes. I only let it run for about 10 minutes, but the current was pretty stable.

If you're starting with a weakened battery, the time required to get back to a charged condition will probably be longer, but my charging current dropped to pretty consistent 1.5A within a few minutes. I only let it run for about 10 minutes, but the current was pretty stable.