Here is a fast field charger for keeping your receiver batteries at peak charge all day. The circuit is very easy and very cheap to build. The entire charger can be built in an hour and will cost less than $10.00 , the amp meter is an additional cost.

A number of these have been built and it does work very well. This fast charger is not intended to replace your normal charger.

Connect the input to a 12 volt gel-cell battery and the output to your receiver pack after every couple flights. Your batteries will be brought back to full charge in a few minutes. When the light goes out the charge rate drops to almost nothing and the charge is complete. (charge time is 15 minutes or less)

Construction is simple, and the layout is not critical. To adjust the charger, connect a 12 volt battery to the input. Connect a digital voltmeter to the unloaded output, and adjust the 5K pot for exactly 5.7 volts DC at the output jacks. The charger is complete and ready for use.
 

Note: Build the circuit exactly as shown. The #67 automotive light bulb is more than just an indicator to tell you when the charge is complete ! It is also the current limiter in the circuit. DO NOT SUBSTITUTE WITH ANYTHING ELSE ! This charger is not intended to be left ON for extended periods of time.

The circuit may be modified to include an amp meter to monitor the charging rate.
 

PARTS:
1 #67 automotive bulb 12 volt, 400 ma
 
Try Radio Shack for the following parts:
1 LM317 voltage regulator
1 5K ohm 10 turn pot
1 220 ohm 1/4 watt resistor (red-red-brown)
1 2700 ohm 1/4 watt resistor (red-vilot-red)
1 150 ohm 1/4 watt resistor (brown-green-brown)
1 SPST toggle switch (ON-OFF switch)
1pr Tip Jacks for charger output connection
1pr Tip Plugs for Charge Cord to RX battery connection
1 Receiver Charge connector for Charge Cord

(Optional) 1 ea. 300 or 500 ma meter