In short, YES. There are no typical values that I have been able to find. The resistance is a function of plate area, condition of the battery, and type of lead-acid battery. Whether it is deep-discharge type or regular car battery enters into the equation. Lead-acid/calcium, such as you would find in a UPS are different yet.
Not much help, but hopefully it helps you understand the parameters you face in arriving at a nominal resistance.
Hi buzzp, your statement is correct, IF the battery is fully charged. As a lead-acid battery ages, more and more sulphate builds up on the plates, which lowers the open-circuit voltage of the battery. This is the same thing that happens as a battery discharges, except with aging the sulphate is such that it can't be re-absorbed during the charging process. So, in other words, you have two separate chemical conditions which affect internal resistance of the battery
