My advice: wade into HKJ’s discharges and djozz’s MT-G2 crash test data - crash-testing a MT-G2 on a copper Noctigon, graph done, mod done and repaired :-)
If a D cell is a tight fit you can’t fit 4xAA. Carriers exist, but aren’t relevant in that case.
6xAA is probably fine. Take a look at the djozz’s data - you’ll see that you are at absolutely no risk of zapping that emitter.