Store ETH wallet on two brand new offline mobile devices?

Hey guys,

I've always had an ETH wallet with a keystore file and a memorized password, but I want to improve that.
Would you consider it safe to buy two cheap brand new phones, disconnect them from the internet, insert a micro sd card and save the keystore on both the mobile phone storage and the micro sd card? Also setting a PIN/Pattern and the keystore/mmenoic password encrypted with a password too.

And place them in my house in two different hidden places.

And I don't intend to use it for anything, but to hold for 10-20 years.

Concerns would be if the storage dies with time?