Just a thought but you could consider weighing the two batteries, find the difference in weight and them compensate by adding some cheap stick on weights to the lighter battery. You can get little stick on weights from any decent model shop that sells rc planes. They are pretty cheap and come in a variety of sizes.
In terms of the wife you just need to make sure she gets a good hobby which you can use to balance it all out just be careful as my girlfriend now owns 2 horses
