Battery should be in right rear IMHO, as close to directly above the rear axle, or slightly ahead of it, as possible. Not behind the rear axle. That location won't show a mistake on the scales but it acts sort of like an un-sprung weight in actual use. Similar to how a trailer would act if you put all the weight behind the wheels instead of on top of them, but on a much smaller scale, of course. The big issue is that most folks don't have the experience to notice a big difference when a battery is moved around. Some do, but most don't.