The IBS is located inside the negative battery cable and sold as one unit. BMW has revised this part 3 times and is currently only selling the 4th generation version. The latest version uses a different harness pinout, so in addition to the replacing the IBS by replacing the negative battery cable, you also need the option harness adapter.
The IBS will not throw a CEL if defective but will throw fault codes into the ECU which can be read during a typical diagnostic scope. Usually a defective IBS can be identified quickly because it will throw many hundred faults when it goes bad. You can replace the IBS without any need for additional coding or updates, simple DIY task but the parts will run around $270.
When you replaced your battery, if you did not replace the IBS at the same time, you would need to have reset the IBS to properly charge the new battery. There are a number of threads on the process to reset the IBS, this is a fairly simple task w/ the right setup. If you did an AGM battery replacement, then in addition to the IBS reset you may also need to code a new amp hours value for correct operation.