If you can read Russian, I recommend Leonid Mlechin's eponymous biography of Lenin. Mlechin is one of the few people who was a successful journalist and historian during both Soviet and post-Soviet times. That's a pretty rare accomplishment for several reasons.

For English-language sources, Robert Service's biography of Lenin (and really all his work concerning the Soviet Union) is amazing, thorough, and well-sourced. Service published this particular book in 2000, which was during a time when many Soviet-era archives were being opened to at least certain portions of the public.

Also, God bless 'em, marxists.org has a whole bunch of Lenin's own writing, translated (well) and available for free online. I know you're specifically after a biography but not much can offer the opportunity to form your own balanced view about the man, in the context of his times, better than the contemporaneous writings of the man himself.

Finally, Hungarian-born Cold War era journalist Victor Sebestyen recently published a biography Lenin: The Man, the Dictator, and the Master of Terror (2017). I've not read it personally, but it was pretty highly acclaimed (so make what you will of that). As Sebestyen's general tone towards Communism in his other writing, and the title of this book implies, it may not qualify as well-balanced in your eyes, but I thought it would be worth adding since it's so new and further archives have become accessible since Service's biography appeared almost two decades ago.

Sadly, the AskHistorians booklist is lacking any biographies of glorious comrade Lenin.