I upgraded from A11 to A15 using the executable M1330A15 (via DOS) and was successful.
Before the upgrade, I left the laptop alone for several months. The battery showed 4 out of 5 pips when tested.
After the BIOS upgrade, the battery behaved differently.
It supported fewer and fewer minutes of powerup time - at first, the battery lasted 10 minutes before shutting down. Now the battery fails to support the M1330. It blinks red (once) and blue (about 5x). The battery shows all five pips when tested.
I hated doing it, but I downgraded BIOS to A14 and then to A10 but I still get the same behavior on the battery. I'm back to A15.
I get 5 out of 5 pips on the battery, even though it will not power up the M1330.
AC adapter is genuine Dell, and I have used a PA-12 and PA-10 (both are genuine Dell). There have been no issues with authenticity. I don't believe the power jack suffered physical trauma.
I wished I had another M1330 for verification purposes. I am very reluctant to spend money on another battery - I fear I will encounter the same results.
What exactly is happening to my laptop and/or battery?
Thanks for reading!