Breakdown of Мой телефон опять разрядился.
Questions & Answers about Мой телефон опять разрядился.
Because телефон is a masculine noun in Russian.
Possessive pronouns must agree with the noun they describe:
- мой = my (masculine)
- моя = my (feminine)
- моё = my (neuter)
- мои = my (plural)
So:
- мой телефон = my phone
- моя машина = my car
- моё устройство = my device
The -ся makes the verb reflexive/intransitive here.
Compare:
- разрядить телефон = to discharge the phone / drain the phone battery
- телефон разрядился = the phone discharged / the phone ran out of battery
So in this sentence, the phone is not something being acted on by another subject. Instead, the phone itself is presented as having lost its charge.
This is a very common Russian pattern:
- transitive verb without -ся
- intransitive/reflexive version with -ся