Learn Finnish: Arvostelija sanoo, että puhelimessa on vaihdettava akku. - The reviewer says that the phone has a replaceable battery.

Vaihdettava is the passive present participle of the verb vaihtaa (to change or replace). It literally translates to 'to be replaced' or 'that can be replaced'. This participle is very often used to create adjectives ending in '-able' in English.

Could vaihdettava also mean 'must be replaced'?

Yes! The -tava/-tävä participle often expresses obligation. A sentence like Akku on vaihdettava typically means 'The battery must be replaced'. However, when used directly as an adjective describing a noun, like vaihdettava akku here, it usually means the action can be done, giving us 'replaceable battery'.

Why does the sentence use puhelimessa on instead of puhelimella on for 'the phone has'?

While people and animals 'have' things using the adessive case (like minulla on), inanimate objects usually use the inessive case (-ssa/-ssä) when they contain a feature or a physical part. So 'the phone has' is literally expressed as 'in the phone is' (puhelimessa on).

How is the word arvostelija formed?

It is built from the verb arvostella (to review, to judge, to criticize). By adding the agent suffix -ja, it becomes a noun meaning the person performing the action: a reviewer or a critic.