berfles ,
It seems you are not aware of how protected cells work ......
They may dim some in use - but if you drain one to 2.5v it's protection will open the circuit, and current can no longer flow thru the circuit to operate the light. It will turn off abruptly , but at 2.5v you should have noticed some dimming.
After you drain one to that point , it should take 8 to 9 hours on the charger to reach fully charged at 4.20v . (you may not be charging them long enough - or it could be a charger issue ?)
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Quote of info. from the link you provided :
snip ..... snip ...
"Ultrafire 18500 1600mah 3.7v
PROTECTED BUTTON TOP
Protected Rechargeable Lithium Battery Li-Ion UF18500
Detailed Description:
This cell is features a button top making it particularly compatible with many flashlight applications.
Rechargeable Lithium batteries are rapidly becoming a very economical way to lower the operating costs of Lithium-Powered flashlights. We offer a number of different options in order to meet any rechargeable needs.
These are Protected batteries.
These
fully protected cells simplify usage with their integrated PCB. Perfect for your single cell application these cells are not for pack building and should not be welded or soldered on which may defeat pr daamage the PCB protection. If you are building a pack please choose one of our other cells and the appropriate PCB.
Features and Benefits
- Unique and New! With integrated PCB Protection!
- Lithium Ion 18500 cylindrical rechargeable batteries
- Internal PCB protection prevents under-voltage at 2.5V and over-voltage at 4.25V.
- Unique PCB design and patent pending.
- Higher energy density and lower weight than other types rechargeable batteries
- Manufactured under ISO9001-2000 to assure quality
- Battery tested based on International Electrotechnical Commission (IEC) standard to ensure capacity, quality and life time
- Lighting or other device needing 3.7V power
- Building portable power device needing high energy density and low weight .."........ snip
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berfles ....
since you like to run your lights till they turn off ......
I would like to take this opportunity to advise you NOT to do a couple of things .......
YOU should NOT :
Buy and use any NON-Protected Li-Ion cells in any MULTI-cell light .
Or DON'T even use Primary cells in a MULTI-cell light / unless you can verify that each cell is EQUAL in voltage when you put them in . ( what we call - "matching" cells) You need some type of testing meter to do this.
Only run a light till it turns off - if you are using common consumer batteries, such as Alkaline.
The batteries you are starting to use NOW ....... have Safety concerns in their usage.
.