My high-end charger is a Maha/Powerex C9000, and its input is 12 VDC. I use it for specialized tasks like battery forming.

However, my everyday driver is the much-underrated Duracell CEF23DX4N mobile charger. I have three of them. A little slower than the Maha, but it does have individual charging channels and comes with a DC lighter cord. I find it does a very good job. And there's still stock around -- I see them at occasionally at Best Buy and Staples for $20.