my friends Prius only has 1 key left, it drains the battery like within 1 day (using Duracells) what's the best way to fix this?
Partially depends if its a wireless smartkey or a traditional insertable key. Either way I would immediately go to a good locksmith (save a few dollars) or the dealer. When your key fails it is more expensive to replace and you are likely to need a tow. Having two is always smarter. If you lose the only one that works its the same more expensive situation.