MacBook 1,1 Displays error on boot, requires PRAM reset each time

Hello all,

Have a MacBook 1,1 model here in excellent physical and working condition - save for this issue.

When I turn on the MacBook after it's been off for at least an hour or so, the Gray screen appears, Apple logo shows, but then a pop-up box displays telling me to power off my Mac and restart. This keeps happening unless I hold down the keyboard keys that reset PRAM, and then the Mac boots normally. I can then shutdown and re-start many times afterwards without any issue.

- This happens on AC or Battery power
- Have tried different AC adapters and Batteries - same condition
- Mac has after-market RAM, 2GB installed total
- Apple HD seems original, in good condition after disk check, and I've re-installed the OS from a clean slate. No change (and this issue also happened before I re-installed the OS)
- No evidence of any spill of physical damage, took the laptop completely apart to review.
- Once Mac is booted, works perfectly - no slowdown or kernel panics.

So... am I in need of a new PRAM battery to resolve? This laptop is after all from 2006/early 2007.

Thanks -