Press the keys *3370# to activate hidden battery power on your mobile phone.

This "tip" is totally bogus. You cannot activate hidden or reserve battery power by keying in *3370# or any other code sequence. The code '*3370#' can be used on some Nokia models to activate Enhanced Full Rate Codec (EFR). Ironically, since this code activates the best sound quality on the phone, the change will actually reduce the length of time that the battery will last before recharging is required – in practical terms the complete opposite of what the tip suggests.

Entering the code has no effect at all on brands of phone other than Nokia.