Si se me olvida enchufarlo, me quedo sin batería.

I

Breakdown of Si se me olvida enchufarlo, me quedo sin batería.

• si: if
• lo: it
• olvidar: to forget

Questions & Answers about Si se me olvida enchufarlo, me quedo sin batería.

Why is it se me olvida and not me olvido or just olvido?

Spanish has an “accidental se” construction to present things as unintentional: se + (indirect object) me/te/le… + verb (3rd person). With olvidar, it’s very common: Se me olvida… ≈ “It slips my mind…”.

• Me olvido (de enchufarlo) is also correct and more directly “I forget (to plug it in)”.
• Olvido enchufarlo is grammatical but sounds more formal/blunt (“I forget to plug it in”).

Who is the grammatical subject of se me olvida enchufarlo? Why olvida and not olvido?

The subject is the infinitive clause enchufarlo (“plugging it in”). Because that clause is treated as a third-person singular subject, the verb is olvida, not olvido.

Can I say Si me olvido de enchufarlo instead? Is there any difference?

Yes. Me olvido de + infinitive is perfectly fine: Si me olvido de enchufarlo, me quedo sin batería.
Nuance:

• Se me olvida… frames it as unintentional/it slips my mind.
• Me olvido de… is a straightforward “I forget…”.
  Avoid mixing them: se me olvida de is incorrect.

What exactly does the do in ?