Hi. I have a Superstar 40 with a Futaba T4VF 72MHz radio. The charger for the radio rx/tx is a simple transformer, and the tx has an analogue charge indicator. I have no idea how long to leavethe rx and txplugged in to charge the batteries. I also don't really know how long the batteries should last once charged. Up to now I've just been recharging them after each flight, and leaving them to charge overnight. Any advice would be appreciated, thanks.</p>

the charge time will depend on the milliamperes of the battery and the output amps of the charger. for example my RX battery is 1600mah, the output of my charger is 150mah. is it will take 10.6 hours to fully charge my battery if it is completely dead.

G'day Mate,
Be aware, to charge a fully discharged nicad or NiMh battery, you need to put in 140% to get 100% out, it has to do with losses inside the cells.
Have a look here, http://www.hangtimes.com/redsbatteryclinic.html
For all your battery info.

Hey Al! How are ya? Good to see you on RCU!

Regarding batteries and charging. Alan is 100% correct. There is overhead when charging batteries, meaning you just can't put in 1000 milamps (1 amp) into a 1000 mah battery and expect it to be fully charged. There are resistance losses in the wire, and internal losses due to heat in the battery pack and charger, so, as Alan said, 140% to charge 100% is more realistic.

There should be some indication of the capacity of your batteries and some indication on your charger that says what the output current is. Do the simple math and add 20 to 40 percent to that and you will know how long it should take for a FULLY DISCHARGED pack to recharge to capacity. Partially discharged packs will not take as long. But, if this is a typical wall wart type trickle charger, then it won't matter if it stays on longer than your calculated time. If it is a fast charger, then closely monitor the charge rate and stop it when it is fully charged.

Many, if not most, of the fast chargers will switch to trickle after a full fast charge is completed, but some will not. You have to check to see what your charger is capable of.

I know.. I know.. you said transformer, but a transformer with a couple of diodes is all a wall wart charger is.

CGr.

Overnight, in most cases is good. 12 to 14 hours won't hurt. Most wallwart (transformer on the wall) chargers charge at 50 or 60 ma and would be a trickle charge on the average 500mah to 700mah packs.
The other issue is what condition is your battery in and how well does it hold a charge. For that you will need a way to check your battery at the field between flights.
I mostly use Voltwatch II installed on my plane
http://www3.towerhobbies.com/cgi-bin...?&I=LXHDJ2&P=7
Some people like to use expanded scale voltmeters such as:
http://www3.towerhobbies.com/cgi-bin...?&I=LXWDZ5&P=7
Even a low capacity battery in the 500 to 700 mah range, in good condition and starting with a full charge should supply enough power for 4 or 5 average flights on a typical glow trainer before needing a recharge.