Each battery change is a break in the power supply. This means that the Accu-Chek Compact Plus meter does not know whether or not the drum compartment cover was opened and the test strip drum was changed. In this case the meter assumes, for safety reasons, that the drum compartment cover was open and reads the code again. It accesses the first chamber and if this is empty the meter identifies the test strip drum as having been used.
Another old, used test strip drum could have been inserted during the battery change. That is why, for safety reasons, the meter now prompts the user to carry out a control test.