Battery drain is evidently an issue with some head units as it'll kick on the backlight when an approaching vehicle is detected. A guy in my club connected to my Varia during a century and he had to disconnect after a few hours because he didn't think that his 520 would make it the whole way. I believe that some here have experimented with backlight settings and have deceased the drain rate significantly.

I recently picked up a 530 (after using a Wahoo Bolt for the last two years) and was happy to see more than acceptable battery life when using the Varia; I think that it would easily cover back-to-back centuries.