Agreed that you should keep the battery box.
Is there a reason you are sticking to cardioids?
I prefer omnis because to me they have a more natural sound and are more forgiving. Cardioids need to be pointed at the sound source, so they may be good in a fixed position, on a mic stand, where they'll shut out audience noise behind them. But if you are clipping the mics to yourself, and not standing precisely still at the right angle, you'll get volume variations you don't want.
The other problem with relatively inexpensive cardioids is lack of bass. The CMC-25 go down to 30 Hz--where if you are listening down there, you'll hear bass lines that suddenly seem to jump an octave because the mic isn't picking up the tone, just its overtone. CMC-26, 40 Hz, worse. CMC-2, 50Hz. Those would bother me. The bass isn't rolled off, where you could restore it if you wanted. It's not there.
Whereas you can get inexpensive omnis that go down to 20Hz. For many years I happily used the SoundPros BMC-2. I've lately moved on up to Church Audio CA-14, but the BMC-2 is still a good place to start. If you're using them regularly, buy the 3-year warranty because you can get them replaced. If you can be patient, keep an eye on the Sound Pros site--he sometimes cuts the BMC-2 price in half. And if you can be really patient, order some Church Audio omnis.