I have a Tower Hobbies Tower 40 trainer. It comes with a TH Tx with NiCd batteries.

My question is: How often to charge the unit?

With NiCd, I am worried about "memory" so charging after each flight day seems bad (especially if only one flight). But waiting for a loss of power during flight is bad too.

For example, had it out yesturday for only one flight. Will take it out next Saturday. Should I charge again? Wait for x number of flights?

Should the Rx battery in the plane last the same/more/less than Tx (which at least has some lights for warning).

(Note the TH Tx does not have a meter...just red and green lights with a warning flashing at low power).

Charge the nite before each fiying session. Memory is not the problem it once was with modern batterys. Charge both tx and rx. The only time you have to worry about too much charging is when you charge more than 10/c. That's the rate of the chargers that typicaly come with the radio set.

Ditto. The way we use our batteries along with the modern NiCD technology virtually eliminates the possibility of memory.

What has changed with NiCd to eliminate the memory?

I have not used NiCD is 5 years having switched all home AA over to NiMH.....

Lack of memory effect has more to do with how we use our batteries than the technology advances of the battery itself, although there are a few. Memory really only happens when you discharge a battery to the exact same point with the same discharge rate and then charge it exactly the same amount each time on a regular schedule. For example, the aerospace industry would have issues with NiCd batteries in satellites. The satellite would drain the battery exactly the same amount until it came around in orbit into the sun to be charged. The battery would be charged/discharged exactly the same amount because of the consistency of the orbit. That's when you'd have memory issues. We never use our batteries in applications that have/require this precision and consistency.

Google "R/C battery clinic" lots of good stuff there including your question.

[link=http://www.rcbatteryclinic.com]www.rcbatteryclinic.com[/link]