Psion Revo 16mb. Plugged it in and it turned on briefly. Guessing the battery is a goner. Used the Symbian operating as used in the classic Nokia's from the 90s. : r/vintagecomputing
Psion Workabout PRO - Backup Battery - WA3019, 18,00 €
Psion Revo Plus Full Device Specifications | DeviceBeast.com