Welcome to the forum.
Those are multi-description codes that are ECU type-specific. As this is likely a MM-IAW 6LP.
P1153 - Marelli 6LP. Malfunction. Throttle stop learning.
P1621 - Marelli 6LP. System anomaly. Safety. [That may mean that it was in limp-home mode.]
The most likely cause of those codes is the already-noticed battery voltage problem.
Replace the battery; check for drains/charge rate and then carry out the throttle learning procedure that your scanner supports. If that doesn't work; download the latest software into the ECU.
Also bear in mind faults that don't leave codes - like the crank sensor, or it's plug and fuel pump faults. A look at the plugs can also be informative.