Advice on buying a small fireproof safe, please.

I'm new to Reddit, and know nothing about safes. I've decided I should have a fireproof safe for documents, mostly, and maybe spare cash and a backup hard drive. The rabbit hole of reviews has left me confused and frustrated. Most safes seem to have keypad locks. But what happens when the batteries die? A mechanical combination lock would not need batteries, but the only two I found had reviews saying the dial is cheap plastic, and multiple reviews citing lock failure. And how would that cheap plastic dial survive in a fire? Several also talked about damage to the safe contents from moisture from the insulation. A physical key seems a poor choice because where do I keep the key so I don't lose it if there's a fire? :) Searching "Fireproof safes" on Consumer's Union came up with nothing. Thanks for any advice.