servo current drain rate

How long you can safely fly on a "fully charged" 4.8V rx battery depends on TWO things; the actual drain on the battery and the KNOWN capacity of the battery in mah... The BEST way to be sure you're safe is to obtain ahd use an "ESV" (expanded scale voltmeter). Use it often...
The ESV should be a standard addition to your flight box, and it's frequent use is the best insurance you can get against losing a plane to a dead flight pack.
Just leaving the Rx on by itself, with no tx signal, to discharge the pack is not good, for two reasons... One, the rx could pick up spurious signals that could cause the servos to overrun their limits, causing gear damage, and two, you could let the pack discharge to too low a voltage and run the risk of reverse charge of one or more cells when you attempt to recharge..
Invest in an aftermarket charger that has cycling capabilities, and cycle your packs rarely, only to see if capacity is up to snuff.. If you cycle a pack and the cycler indicates 80% or less of rated capicity for two cycles in a row, replace that pack...
Cheers,
Bill

My manual says 8mA(idle) but nothing for full load
Does anyone know? or do you have a method for working how

Good advice.

Servos vary as to how much they draw. If they are properly sized and the linkage is good, you should never get anywhere near the stalled current. Many standard servos I have measured come out near 250-350mA fully stalled.
The BEST way to determine how long you can safely fly is to use an ESV before and after every flight. Pick a day when you can make 5-6 flights comfortably and check the pack before and after each flight. When the needle is at the bottom of the green, stop flying! I would use this as you absolute max as the conditons of each flight can be very different. Make sure you also monitor the transmitter battery as well!

Thanks for the advice paul, Transmitter is ok as it shows voltage on the LCD and alarms if it gets too low, not that I fly with it that low except on the PC flight sim.

One of the problems in determining a max current draw for servos is that it is extremely dependent on the installation and operation of the servo, pushrods and hinges. Correctly installed hinges with minimal friction, properly routed and supported pushrods will result in the lowest posible draw. But one or more crooked or misaligned hinges, pushrods that bind and grab will cause the current level to rise greatly as the servo fights all the resistance in the mechanical path to the surface. An ESV will give an indication of the condition of your mechanical installation as a bad setup will cause the current to rise and the voltage on the ESV to drop markedly.
As others suggested, invest in an ESV and a good cycler and use them. Most importantly, keep a log book of the relavent data so you can develop a history of the battery packs characteristics.
Brian Allen