I need help, I have Flaslight, using dry cell 4,5v 3000MaH, I am confuse where I can find this cell, I bought panasonic dry cell 6v 4500MaH, when I try to conect to the battery, the LED just die in 15 second. I have question, to push down 6v to 4,5v what I have to do? I am blank about electronic
Welcome to blf! Do you have pics or link of the light. not all leds can handle 6v
Wouldn’t 3 x Alkaline batteries (e.g., 3 x AA, etc.) yield ~4.5V?
My flashlight using cree 10w, and already using driver, but I dont know how many volt to the led. What if I using resistor conect to the battery and then conect to the driver, but I dont know what kind of resistor I have use?
wiuld be better if you tell us the model of the light, a picture or a product link. I really cant picture out that light.
gotta show the goods man. show us your LED 
If the emitter’s truly “cree 10w”, then probably you’re looking for a Li-ion battery. Even with that, the light should have a driver circuit that connects between the battery and the emitter, as you wouldn’t/couldn’t safely run the emitter directly from a Li-ion battery (possible, but not likely).
As other’s said, tell us exactly what light you’re talking about or provide a pic.
There are lots of ways to reduce voltage, but if you need to learn electronics to do it. Consider it an education instead of a money saving project.
If you just need a working flashlight, for the prices around, I would just recommend a new one.
If you want the education, you have come to the right place.
Seems like XY problem, please give us more info.
Don’t change the battery, change the emitter!
use a MT-G2 or XHP50, 70 and bingo bobs your uncle.
4,5v 3000MaH does sound like it’s meant to take a lithium-ion cell.
There are health and safety precautions you need to understand about lithium-ion.
You can’t use them like ordinary batteries.
Do you have a ruler?
Can you measure how long your flashlight is?
Can you measure the diameter of the battery tube — outside and inside diameter?
Can you reach down inside where the battery would go with a stick, and measure how long the battery is meant to be?
Look on the outside of your flashlight.
Are there any letters or numbers written on it?
Is there an icon or picture on it?
Where did you get the flashlight?
Can you ask whoever you got it from for more information about it?
My flaslight just local Indonesian product, there no more information about the battery. And I think this company made this flaslight for once used, thypicaly cant be repaired, I dont have much more information about this flaslight. All I know, the battery using 4,5v 3000MaH dry cell, and the problem is I have 6v 4500MaH panasonic dry cell, when I replace the battery, the LED just die a view second. Thank you so much for all of your coment. If I cant find the way to repaired, just iqnore it, I wanna buy the new one again.
Big, fat, .5ohm power resistor scrounged from old electronics parts bin. At 3A will drop to 4.5V but needs to be 10W.
Thank you, I have try this, fat 5ohm old resistor
Look closely at the LED — does it have a brown spot in the middle of the yellow?
If so the 6-volt battery probably broke it and it won’t light up again.
1/2 ohm, not 5 ohm
By 6-volt dry cell, I assume you have the square camping lantern style battery?
The only 4.5V I’m able to find is listed as a 3R12?
Since I don’t know anything about your flashlight, it would be difficult to say, but an inexpensive driver circuit like this one:
http://www.dx.com/p/18v-5w-cree-circuit-board-for-flashlights-16-8mm-5-5mm-26110
…would step down the higher voltage and let you power a single emitter at about 1.25A. If your LED is a true Cree 10W, then I would expect it to be an XM-L T6 or similar. This driver would not give you full power, but would still be enough to get lots of useable light.
This sounds like a first host for a DD XHP50 build? 
If you can take one cell out of the 6V battery pack, that would make 4.5V. 1.5 volt per cell. I am not sure how to reconnect that unless you can solder. The missing cell has to be replaced by a wire to restore continuity.
I have used big fat resistor 5ohm, and it doesnt reduce volt, it still 6v. I have new question, what if I change the LED using cree XHP 70 32w. It works on 6v