Intro
I got my first flashlight a few days ago (Review) and needed a few 18650 batteries to go with it. I extracted 9 LG 18650 from a laptop battery pack but wanted to try/test protected batteries.
I just received two Sanyo 18650 2600mAh from DX paid 8.36USD. Ordered 18th, April. Received 14th, May.
Presentation
The protective case arrived destroyed but it did its job, the cells are in perfect shape.
Out of the box voltages:
Cell 1: 3.778V
Cell 2: 3.777V
Excellent!
Both cells are stamped with the code S04A which means the inner cell was produced during the fourth week of 2014. Very good considering they had to go to an other factory which added the PCB…
The cells are 67mm long without the button top, which adds 1mm.
The added button top has vent holes, but they are quite small.
LG cell (unprotected) surrounded by Sanyo (Protected):
PCB
The PCB is on the positive side, enclosed in a strong black plastic case. The whole thing is held together with a very thin clear heatshrink. With the PCB on the positive pole there is no need for a wire to go to the negative pole so the cell is probably thinner than cells with PCB on the negative pole.
The PCB over current trips at:
Cell 1: about 2.5A
Cell 2: about 5A
I believe that the PCB of cell 1 is defective. (or is it a different PCB?)
Both PCB need to be placed back in the charger when over current is triggered.
The PCB under voltage protection trips at 2.5V and doesn’t reconnect when the load is removed. 2.5V is too low to my taste, I would rather see a cutoff at 3V as it only reduces capacity by 30mAh and increases cell longevity.
Measured internal cell resistance (DC) is:
Cell 1: 132mohms
Cell 2: 94mohms
LG cell for comparison: 78mohms
With cell 2 fully charged and a load of 3A that means that the voltage sag is 0.282V which means that there is about 0.8W of power dissipated as heat in the cell/PCB. At 4.5A it’s 1.9W.
Capacity tests
Conditions:
-Ambient temp is 20°C
-Cells are charged to 4.20V
-Cells are discharged at 1A down to 3V
-Test is performed using accucel 6 hobby charger. I know for a fact that it is inaccurate, so below is the result of the LG cell to compare.
LG cell: 2.59Ah
Sanyo cell 1: 2.59Ah
Sanyo cell 2: 2.61Ah
How do they hold their voltage? I have no way to get nice discharge curves. However after emptying the cells I put back 500mAh back in each cell and the voltages (OCV) were:
LG cell: 3.60V
Sanyo cell 1: 3.75V
Sanyo cell 2: 3.76V
This clearly shows that at a same SOC the Sanyo has a higher voltage.
Holding a voltage higher is better as it means that the energy (Wh) contained is higher. It’s also good for LED flashlights using linear regulators as it’ll keep 100% brightness longer before dropping.
Sanyo is clearly better on that point. And that proves to me that the cells are genuine.
Conclusion
Pros:
-Genuine Sanyo cell which holds its voltage high during the discharge.
-Over current protection is set just right
-Quite small in diameter and only 3mm more in length compared to non protected batteries
Cons:
-Internal resistance is quite high. That’s the drawback of protected cells.
Would I buy this again?
At 8.36USD it was a great deal so I couldn’t resist. But at 12USD I wouldn’t buy it as I can get decent (LG) cells out of a laptop battery pack for about 3USD a piece or even free if someone gives me his old pack…
If you really need protected cells however, I would recommend these if you don’t want to spend big bucks on Panasonic 3.4Ah.
Final note:
I will probably use these to power electronic things that I’m building/modifying as it will limit damage when the inevitable short circuit happens…
Please feel free to comment the way I did this review as this is only my second one.