The Suffrage badge is awarded to a user who casts 30 votes on questions and/or answers in a single day.
The Vox Populi badge is awarded to a user who casts 40 votes, the daily limit. It is possible that a user won't be able to use 40 votes in a day as is explained here.
Do we really need both badges? Don't they reward effectively the same behaviour? If you haven't already received the Suffrage badge, won't it be awarded to you on the same day you get the Vox Populi badge?