Most helpful positive review
59 of 65 people found the following review helpful
Awesome 18650 protected cell
on June 28, 2010
This is a very decent 18650 secondary cell (not a battery) with the Ultrafire brand. Not sure if the 3000mAh claim is true, but I can vouch for the fact that it lasts a bit longer than other cells I own (a few Trustfires, a few Ultrafires and a few Tenergys, rated between 2400mAh and 2600mAh).
The button top feature means that they will work well in spring-less flashlights (no need for a magnet-button).
The protected feature means they have a chip on board that protects it from over-charge and under-discharge. If over-charged (over 4.2V in layman's terms) the cell overheats and may explode (it's called "thermal runaway"). The explosion itself is a chemical rupture-explosion, a very nasty thing. If under-discharged (used under load until it drops under 2.75V, in laymen's terms), a chemical reaction makes the cell unstable, dangerous and unusable. The chip onboard should protect against this. If you are running a flashlight until it gets dim and hits the low treshhold, the cell shuts down - you should throw it away. I never run my cells below 3V, and my charger takes care not to charge more than 4.2V.
Never leave the charger unattended overnight. Put the charger in an area where a potential explosion does the least damage (a fireplace, if you have one, is great). When the little light on the charger turns green, take it out. Get a voltmeter and measure. Under no load, the voltage should be 4.0-4.2V. The nominal voltage is 3.7V, that's what should read when the cell is under load. Let is sit 20-30 mins after a fresh charge and before using it - this cools it and "settles" the chemistry inside.
Your charger should also protect against overcharging. Naturally (duh...), you must use a charger made for charging 18650 cells. This cell will not even fit in a Wallmart/Kmart/Target found charger. This cells are not available in retail. Their size is different from AA, AAA, C, D, etc... And yes, you would charge a Li-Ion cell with a... Li-Ion charger.
As far as compatible chargers, just type 18650 in the Amazon search and go down the list. The DSD charger is very popular and praised for it's simplicity, you also can't go wrong with Tenergy products, it's a US company with a lot of pride in quality control. Personally, I use a Pila charger and I have several DSD ones.
Amazon did not do anything wrong here, description is fine and all specs are accurate, so please disregard the previous rant against Amazon (and not related to the product).
This cell is great. If you know what a 18650 is for and what it does, then buy this with confidence. If you don't know what this is, please step away from this page, this is not for you and you might get hurt - chemical fire is very nasty.
I use these cells primarily in hi-power Cree led flashlights. If you want to build a pack (for example, in robotic applications), you're probably better off going with unprotected button-less. After you solder your pack together (careful not to overheat - heat is another Li-Ion fire starter) you should attach a custom made protection circuit to the entire pack. The protection circuit is a must-do requirement!
Most importantly - use common sense. If you don't have one, do not buy/use these cells.
Price is a bit steep, but if you want crazy life-on-the-edge performance, and more importantly, you know what you're doing, then this cell is for you.