STLs, or small transmitting loops. Also known as magnetic loop antennas. Diminutive in size, but big on performance!
Loading coils add series inductance to the antenna system, allowing for a shorter radiator. Also permits the use of several bands without the need for a matching unit (tuner).
I use a variety of batteries I have assembled from LiFePO4 (lithium iron phosphate), Li-Po (lithium-ion polymer), and Li-Ion (lithium ion) cells. When it comes to batteries to run your portable setup, the only right answer is LiFePO4!