Without a working PRAM battery, a vintage Macintosh (like the Plus, SE, or early Power Macs) "forgets" its settings every time it is unplugged. This means losing time, date, and sometimes custom SCSI settings, which can hinder the boot process.
Many early Macintosh computers, such as the Mac SE, have soldered PRAM batteries. While designed to last for many years, these batteries are now decades old and prone to leakage. MACINTOSH PRAM BATTERY
Getting Started With Your Vintage Macintosh – Garrett Fuller Without a working PRAM battery, a vintage Macintosh
If your vintage Mac is suddenly living in 1956 (or 1904, 1984, etc.) every time you turn it on, the PRAM battery is likely dead. 2. The Danger Component (Soldered vs. Holder) Without a working PRAM battery