Sounds like the system has different sleep modes for battery vs AC. Since the above list mentions both S3 and S4 you might have some luck changing the sleep mode in the BIOS. Sometimes it's named strangely like "Windows" vs "Linux" sleep mode, but you can try both. The BIOS might also let you choose a different sleep mode for when plugged in.
Sounds like the system has different sleep modes for battery vs AC. Since the above list mentions both S3 and S4 you might have some luck changing the sleep mode in the BIOS. Sometimes it's named strangely like "Windows" vs "Linux" sleep mode, but you can try both. The BIOS might also let you choose a different sleep mode for when plugged in.