Cottonwood
Roadster#433, Model S#S37
That Battery Tender is only 1.25 Amps. With the thirst of the Vampire, you really want a smart charger that can put out more than 4 Amps to keep up.
Here is my choice: Amazon.com: BatteryMINDer 12 Volt 2/4/8 Amp Wet/Gel/AGM Battery Charger. It's multi-stage, temperature compensated, and will put out 8 Amps. The only problem with this choice is that you have to select "AGM" and 8 Amps every time you plug it in.