text: Buy an MPTT charge controller more efficient and better on the battery. Renogy has an ebay outlet, with pretty good discounts on clearance, open box and returns.
  These are stereo transformers that are intended for car radios. There are many similar on Amazon and other sites, all very unpricey. To connect one side for balanced, chop off the female phonos and solder the wires onto pins 2 and 3 only. Chop off right up at the females as the tails are very short and don't leave much for soldering a second time after you forgot to put the boots on the first time - so I've heard. Alternatively there are versions with the transformers in a box with phono sockets instead of flyleads. The impedance mismatch will only affect the level and with a car radio you'll be setting that with the volume knob anyway.