I was just reading on someone else's flashlight blog that had a bunch of flashy pictures that explained a lot about the components in a flashlight and very little about flashlights. The writer explained that a good flashlight will always light and should never need to banged against your hand to work. Total Bullocks.
Once again all flashlights are about electrical connections. Any flashlight that depends on spring loaded contact will have corrosion issues and banging it against your hand can help it work.
WTF does that mean?
Most, not all flashlights, depend on wire springs that provide pressure to improve electrical contact between the various parts of the flashlight. The tension of the spring is important. The stronger the spring the more likely there is to be contact between the various components.
Lets look at a typical 2D cell flashlight, cheap, expensive, whatever. The vast majority have a wire wound, helical spring, at the "bottom", two batteries, a switch, a bulb holder with a metal plate on the bottom and a bulb.
Everything made of metal corrodes, slowly for some things, very slowly in the case of gold and iridium. The spring, the tops and bottoms of batteries, the metal piece on the bulb holder and even the body of the bulb. That corrosion creates resistance. The resistance causes the flashlight to stop working. People used to carry steel wool or a scrap of leather to clean flashlight connections. The corrosion resistance is better these days so people don't do that as much.
When you bang a flashlight against your hand, any kind or brand or expense of flashlight, the rubbing between the various components can scrap away corrosion and make the flashlight work.
Here is the funny part, corrosion depends on the materials used, the amount of humidity and if the moisture can reach the surface. A cheap flashlight with cheap batteries and a cheap bulb can end up having nearly "perfect" connections which prevent the corrosion from forming. An expensive flashlight with good batteries and a bulb can end up having poor connections. The issue is manufacturing variables.
Realistically the probability have having excellent connections is better with a well made flashlight, like a Maglite, good batteries like Duracells and Maglite bulbs is better than a cheap flashlight.
Lets toss in a way for you to build a really bright, long lasting LED flashlight fairly cheaply.
First thing you need is a decent AA flashlight with a standard PR style bulb. There are lots of these, buy one you like the looks of, that looks like it has a good switch.
The next thing you need is 2 14500 Li-ion batteries. These are 3.6 or 3.7 volts. These can run some money, I get mine on e-bay fairly cheaply. Get 4 and a charger if you use your flashlight a lot.
The last thing you need is a really good "3 watt" LED bulb. You can buy these on Amazon, SuperBrightLEDS.com or even at your local Walmart. The bulb will run you 15-20 bucks. Make sure you buy the bulb that handles up to 9 volts. Some are made for 3.6 volts max.
The 14500 batteries are the same size, about, as AA batteries but they put out twice as much voltage. Two 14500 will put out as much voltage, about, as five normal batteries 1.5v batteries. You could use a bulb from a 5 cell Maglite in your new flashlight and the plastic reflector would last minutes. The plastic reflector will melt. I'm told the Garrity G-Tech cheap AA flashlight has a metal reflector and if so that would be a good thing to have. I have not found one yet.
Put the "3 watt" led in the flashlight you purchased and then put the 2 14500 batteries in the flashlight.
My experience is that when using 7.2v or 7.4v the LED bulb will not melt a plastic reflector as long as you don't use the light more than about 30 minutes at a time and you let it cool between uses.