You are correct on all points.

When to use rechargeables?

1. Obviously, when you have a frequently used device. Saves money, saves having to change batteries (if battery can be charge inside the device, like a cell phone).

2. When you need a big current draw. If you've ever taken a basic electronics course, the first thing you learn about is Ohm's law. Voltage = Current x Resistance. The usual analogy is a water tank: Voltage is water pressure, current is the water flow, and resistance is the size of the pipe. The chemistry of different batteries determines not only their voltage, but also how much current they can deliver at that rated voltage. With some battery technology, if you try to pull a lot of current out of them, the chemicals just can't combine fast enough to deliver all the current, and the voltage drops. Thus, if you try to use alkaline batteries in a digital still camera, which requires LOTS of current, you may only get a few pictures before the battery seems to give up. However, if you measure the voltage, you will find that the batteries still seem to be near the original 1.5 volts. However, the chemicals just couldn't combine fast enough to keep up. By contrast, NiCad and NiMh can deliver amazing amounts of current at their rated voltage. They are said to have a low internal resistance (i.e., a large "pipe"), but what this means is that the chemistry used in these cells just simply combines faster.

When NOT to use rechargeables.

1. When you have an INFREQUENTLY used device. This isn't just the opposite of number 1 in the previous section. There is another reason for this, and that is self-discharge. All batteries eventually lose their charge, but there is a HUGE difference in how quickly this happens. At one end of the specture are Lithium batteries (not to be confused with rechargeable lithium ion batteries). These can sit on the shelf for a decade and still retain most of their charge. Alkaline batteries have shelf lives measured in years. However, NiCad batteries self-discharge in a matter of a few months. If you haven't used the device for half a year, the batteries will probably be dead. NiMh (nickel metal hydride) are much, much worse -- the worst battery of all -- when it comes to shelf life. Many of them will lose almost half their charge in the space of a month. No big deal for a laptop that stays connected except when you are travelling, but a big bummer if you put them in a calculator that you only use once in awhile.

2. Long use before quitting. In a few applications, non-rechargeables will seem to quit before their rechargeable counterparts (see #2 in the first section). However, in reality the rechargeable battery of the same physical size always has less total energy and therefore, unless you run into the current problem with a device that requires huge amounts of current (see #2 in the first section), the non-rechargeable will always outlast a new, fully charged rechargeable. Thus, in a wireless mic application, where you don't want the thing dying in the middle of a shoot, you should always use fresh, non-rechargeabel batteries.