The useful life of 1.2 NiCads & NiMh's?

It is most unlikely that you will find Nicads around now. Due to health and safety, they have been replaced by NiMH, which are nowhere near as good, although they have the same physical size, voltages, and currents.
NiMH do NOT hold their charge for very long - due to the chemistry, they 'leak' up to 50% of a full charge in a month, even if not connected to anything at all.
Also - the bigger the capacity, the smaller the burst current they can deliver, although they can deliver a small amount for a longer time. If you over-charge, or over-discharge them, current-wise, they can get VERY hot, to the point of exploding. (They also get hot as they near the full charge!)
If you regularly fast-charge them, you shorten their working life, as well. (The number of charge-discharge cycles).
There ARE some good NiMH cells, though, look for the 'Hybrid' ones, which do not self-discharge, and can hold a full charge for up to a year. Naturally they cost a bit more.
A normal 'cheap' NiMH cell, left uncharged, and not connected to anything, will eventually (about 6 months) run itself down to the point where the chemistry breaks down, and it will not charge at all, or if it takes a charge, it cannot deliver much current.
What happens when you 'pull' current from a cell is - it's voltage drops, and the harder it has to work, the more the voltage drops. When the load is removed, it rapidly recovers again, so if you put a test meter on the terminals, it will show a full charge, or nearby, so the meter is really telling lies! The only way to really test a cell is to put it on load, and measure the current flow and the voltage AT THE SAME TIME.
If you are using NiMH in anything critical, it is best to replace them with new, on a regular basis.

lipo and rx - that's easy - just use a UBEC between the lipo and rx, it is just the same as using a speed controller for electric flight, which in the smaller sizes, has a voltage reduction circuit built in, but they are also available as 'stand-alone' units,commonly used with higher current speedo's. (So if the speedo fails in flight, the rx still works!)
Some rx's will operate on a higher voltage than the standard 4.5 - check your manual, but make sure the servos will as well otherwise you could 'fry' them.
The same applies to transmitters - some like the Taranis will happily take a lipo plugged directly in, but you have to remove it from the tx case to charge it. Others need some form of UBEC, ie Spektrum which works on four cells, but the 8 cell Futaba's need more thought.
You could also void your guarantee by doing this.
A good brand of NimH that I use is the Vapex one, they are on e-bay or you can mail-order from
www.vapextech.co.uk/
They also have a good range of chargers!
I have no connection with the company other than as a satisfied customer.

Simon - the main reason for removing a lipo before charging it is the - just in case - scenario - just in case it decides to spontaneously combust - then it can't take the tx with it!
The Taranis set will not charge the lipo through the case socket, so unless you have made a Y lead of JST's, you have to unplug the fiddly little thing from a recess, each time - but they come supplied with a six cell 2000mah nimh anyway, and that will last all day (and a bit!), so you only gain in run-time, with a lipo. (I'm using one! ((Nice set!)) )