Small four cell 4.8V battery of 4 x AAA sized cells is suitable for the Weasel Trek and most F3-RES gliders. The battery comes with a universal (JR type) RC plug.
This battery should be trickle charged at 75 mA for approx 14 hrs. You can make up a charge lead using a 100 ohm 0.5W (or larger) resistor. Charge from a 12V DC voltage source.