Issue is in title:
I can boot only if I remove power to coin battery, internal battery and hold power key for 15 sec then reconnect bats and use AC adapter. Once booted, reboots are fine and I can switch OSes (dual boot win10/ubuntu). When I shutdown or suspend from either OS, a reset (as above) is required. The Lenovo hardware maintenance manual indicates to check coin battery voltage and replace if below 2.5V or if in range to replace system board. Mine was within spec (3 V), but I replaced anyway since it’s a cheap fix. The new coin battery had no effect.
Appreciate any suggestions the community may have.