I get 161 and 163 errors at startup though I changed the cr2025 backup battery a few times (IBM Thinkpad 600E).
Is there anything else that I can do to get rid of the errors?
I think that they are config errors; you could have a bad component e.g. Adapter card, drive etc. causing it. Try using the Diags in the TP600 Hardware Maintenance Manual downloadeable from: www.lenovo.com