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(More customer reviews)UPDATE: This battery (tenergy 2600) holds its charge and compares well against competitors, but does not have a button top which may or may not be of concern if you have a flashlight with more than one cell. Another viable option is the ultrafire which is sold through batteryjunction.com, an amazon seller. The cells are not cheap at 10 dollars each but they are 3000 mah, more than tenergy, have the protection pcb (see below), and have a button top for using in multi cell flashlights like the TK30 Fenix 6 Level 630 Lumen LED Flashlight - back to your regularly scheduled review.
We understand more now about lithium ion rechargable batteries than we once did. I designed products for Logitech to sell in the 100,000 qty that had a built in li-ion battery so the china company who made them came out to Fremont, CA and explained all the good, bad, and ugly about li-ion rechargables (this was 7 years ago)
Back then the good was no memory effect, charge when you want to, and a high terminal voltage of 3.5 - 4.3 V depending on mfgr
The really bad is that just like we know every light bulb will eventually burn out, we also know that during the lifetime of the cell - at any random moment, 1 in 100,000 li-ion cells will either explode or catch fire (back then this made headlines because it usually happened in an airport and most flyers were a little edgy to begin with). The reason was that laptop battery packs often had 10-14 cells in them thus multiplying the odds of a failure to 1 in 10,000 which are pretty good odds that someone's laptop is either going up in flames or making a big boom.
Step forward 7 years
Now we have the protection pcb (printed circuit board). It prevents the li-ion cell from being overcharged or undercharged, both of which are dangerous regions to operate in. PCBs are often gold plated with 50 microinches of hard gold - you can see the underside of the pcb when you look at the tenergy battery. While the positive termial is just metal, the negative is gold. Not realy - inside there is a metal connection to the protection board, and the under side of it has a circular gold spot to make contact with the device springs.
When I bought my 18650 batteries on amazon recently there were 4 amp hour designs available: 2000, 2200, 2600 (these) and 3000. I chose the 2600 because it had the protection pcb in the package over the 3000 which normally I would jump at. It's a trade off - I'm giving up 400 mAh to get the insurance that my cell won't do anything nasty while being charged or discharged. Unfortunately, amazon is not stocking the 3000 Mah (3 amp hours!) version of this cell, with protection pcb, which is a truly excellent battery - it has a button on its positive side so that it works in stacked flashlights. Battery junction dot com carries them, but they are $10 ea for top of the line cells. They also sell the ultrafire charger. Note however that the ultrafire 3000's are a tad bit over the the size limits of the 18650 (18.0 mm diameter and 65.0 mm length is the definition of an 18650) - they fit TIGHT into flashlights which may be why amazon does not carry that cell, but in a tk30 Fenix 6 Level 630 Lumen LED Flashlight they run a LONG time between charges, as do these tenergy cells.
On the subject of chargers, the 18650 chargers out there (both on amazon and on 3rd party sites) charge one cell first then the second cell - usually left first then right) however not all of them indicate which cell is being charged first, so allow overnight so that both cells get charged. The indicator lights are not always right on the cheaper chargers, but the more expensive chargers have good indicators.
I'd recommend any li-ion cell TODAY that has the protection board built in. They are as safe as NiMH rechargables, and preliminary testing of these has shown they are actually about 2800 mAh instead of 2600 but I just got them in the lab and have not been able to draw any statistical conclusions on the design yet other than they are more than 2600. The 3000 Ah ultrafire cells with button tops are comming in around 2950 mah - not bad actually.
Click Here to see more reviews about: 4 pcs Tenergy Li-Ion 18650 3.7V 2600 mAh Rechargeable Batteries (Flat Top) with Internal PCB for flashlights and others
Applications * Lighting or other device needing 3.7V power * Building portable power device needing high energy density and low weight Warning * Use special caution when working with Li-ion cells, they are very sensitive to charging characteristics and may explode if mis-handled. * Make sure user has enough knowledge on Li-Ion rechargeable batteries in charging, discharging and assembly before use. * Put the batteries in fire-proof container in charging * Do not put batteries on wood surface or carpet when charging * Never leave battery un-attended when charging * We are not resopnsible for damage if there is any modification of the batteries in form, shape or made into packs * We are not responsible for any damage caused by misuse or mishandling of these Li-Ion batteries Product Specifications * Capacity* Nominal 2600 mAh, Minimum 2450 mAh * Internal PCB protection prevents under-voltage at 2.5V and over-voltage at 4.25V. UNIQUE INTERNAL PCB! * Dimensions: Diameter 18+/-0.2 mm Height 66+/- 0.2mm * Weight (Typical) Approx. 46 g yes * Nominal Voltage: Average 3.7V * Cut-off Voltage: 3.0V * Internal Impedance: less or equal to 180 milliohm (with PTC) * Cycle Performance: 90% of initial capacity at 400 cycles * Cycle life: > 500 cycles * Charge: Current = 0.5C mA Voltage = 4.2 V End Current = 0.01 mA * Discharge: Current = 0.5C mA End Voltage = 3.0V * Max. Charging current: 1.5C ma * Max. Discharging current 1.5C ma (for continuous discharge) ##Note: If using for Flashlights that uses 2 Cylindrical 18650 Li-Ion Cells.
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