Look on the side or the front of the wall wart charger. It details the output current for each line (4.8 and 9.6 volt charge lines). That current is displayed in mili-amps. You relate that directly to your battery.

For instance: 1000 mah battery and a 100 mah charge port for the RX. (same applies for the TX battery, by the way).

So, 1000/100 = 10. So it will take a full 10 hours to fully charge a fully discharged battery, plus about 20% or so for overhead, so figure 12 hours for that 1000 mah battery to be charged with a 100 mah charge source current.

There is no real way to know how much your battery has discharged after a flying day, suffice to say that it has discharged. You can guess, but why take the chance. So, just figure to charge it for 12 hours (as shown above) ummm... overnight... perhaps (does that sound familiar by any chance? ) and you just cannot go wrong. Once it is fully charged, it will revert to trickle and maintain.

Futaba claims that their current draw for the TX is 170mA. I would assume that's per hour, by the way. So, they supply a 600 mah battery. Do the math. 600/170 = 3.5 hours of use.. well, that is if you want to trust that it will be ok for 3.5 hours of use. The point is you have lots of TX time with the 600 mah battery supplied. The charger looks like it's TX port is 170 mah. What a coincidence!

Charge it overnight and be safe.

CGr.