After thinking about it some more, run the Varia through an app on your phone. Carry/use a battery pack if needed for the phone. Maybe that frees up battery time for the bike computer. Try to get the mapping sorted out on current bike computer. If that doesn't work, then on to an even more expensive bike computer with even more features you don't need/want.
I have a similar situation. I have a GPS watch I use. Phone is in middle jersey pocket. The watch is not a Garmin. I don't want to engage in the Garmin ecosystem. I'm thinking about a Varia. If I get one it means using it through a Garmin watch or something mounted on the bars. The phone would work, but reduce battery life. So would the Garmin bundle display unit. I don't care for either solution. I'll probably end up emitting a beep myself every time I hear a car. That will simulate the Varia and determine if it's going to annoy me or not.
Full disclosure: For me, Garmin is one of the Evil Empire companies in line with Apple, Trek, Nike, etc. Why? I'd have to think about it. Maybe it's tied to Lance. Maybe not.