M: The battery in this portable computer must be dead. Do we have another one / a spare (one)? [It is not wrong to say "portable computer", but realistically one probably wouldn't bother with the word "portable" in a situation where it's obvious to both parties what you are talking about.]
Just a further note on "Maybe I can find one" versus "Maybe I can find it" which I didn't pick up first time round.
"Maybe I can find one" suggests that the speaker is unsure if they have any spare batteries (or how many they might have), which seems to fit with the question "do we have...?" and the response "let me check..."
However, the original "Maybe I can find it" is possib