I have found in cases where I am moving a lot of components around that I need two fairly detailed diagrams, one for before, one for after, with every piece that moves detailed as to weight and distance from cg. I use + for nose moments, - for tail moments. When you get an initial trial balance with ballast at one end or the other, then all your changes in the + and - column need to come out to zero after you've made all your changes. This is more like accounting than physics.

These measurements and calculations need to be accurate, but not necessarily precise, since you can use your battery as a wild card, placing it after every other change has been made for final tuning. In fact, you might just leave the battery out of all preliminary calculations. If everything you change works perfectly, then just put the battery right at cg. If you're off, fix it with battery. If you're way off, use two batteries in redundant hookup. This also facilitates further balancing adjustments based on flight trimming.