As this is the first full battery review that I have conducted, I think it is worthwhile to quickly list the equipment used, and briefly explain some of the measurements taken.
Equipment
For consistency of results, batteries were always charged on the same charger, which was a Jun-si iCharger 106B+. Internal resistance and discharges were both carried out on the same charger, in this case, an iCharger 208B. Two chargers were used for convenience, in order to speed up the testing process.
Dimensions were measured with a Precision Gold digital caliper, and weights measured with a Neva 50gram digital scale, said to be accurate to 1/100 gram.
Voltages were measured with a Precision Gold WG 020 Multimeter. While I do not have the means to calibrate this, I also have a UNI-T UT60 multimeter, and measurements on the two correlate.
Internal resistance measurements, and discharges, were carried out using approximately 12" lengths of 16AWG cable, with either a crocodile clip hardwired to the cable, or a 10x10mm high strength, rare earth magnet soldered to the wire. Each wire is terminated with a gold plated banana plug for connection to the charger. Shorter wires would have reduced IR further, but could have placed strain on the wires, and increased likelihood of the magnet or clip being pulled off the battery.
Measurements
Some of the measurements that I will be taking may seem a little pointless, but add to the overall information available, and certainly do no harm. For instance: -
Initial voltage - this is the voltage of the cells as I received them. It doesn't mean a whole lot, as the person who sold you a cell could take a 0V cell, with a tripped protection circuit, give it a storage charge, and then send it to you, and you would be none the wiser. Still, this would at least indicate that the person knew something about li-ion cells. Certainly, no-one wants to actually receive a cell with a very low voltage or a tripped protection circuit.
Capacity from initial charge - even less important, but with todays high capacity cells, I personally find it interesting just how much capacity is available even from the storage charge. In the case of cells with lower than normal termination voltage, I can also use this step to get an idea of the difference in capacity when discharging the cell down to 3.0V (this will be my normal termination voltage when running a discharge), and when discharging it to the manufacturer's stated minimum termination voltage.
With no further ado, lets do some testing.
Cell: Xtar 3100mAh 18650
Base cell: Panasonic NCR18650A
Basic chemistry: ICR (LiCo)
Charge voltage: 4.2V +/-0.05
Discharge voltage: 2.5V
Purchased direct from Xtar, for $26 including shipping.
Results at a glance - initial (please check my final results further down)
|
Cell 1 |
Cell 2 |
Initial voltage |
3.625V |
3.630V |
Quoted length |
68.5mm +/- 0.5 |
|
Quoted width |
18.4mm +/- 0.1 |
|
Measured length |
69.02mm |
69.00mm |
Measured width (max) |
18.68mm |
18.58mm |
Weight |
46.48 grams |
46.37 grams |
Capacity from storage down to 3.00V |
1131mAh |
N/A |
Capacity from storage down to 2.50V |
N/A |
1282mAh |
Internal resistance after storage charge |
123mOhm (magnets) |
126mOhm (magnets) |
Capacity from 4.2V down to 2.5V @ 0.6A |
2984mAh |
2983mAh |
Capacity from 4.2V down to 3V @ 0.6A |
2877mAh |
2855mAh |
Capacity from 4.2V down to 3V @ 1.0A |
2806mAh |
2761mAh |
Capacity from 4.2V down to 3V @ 3.0A |
2284mAh |
2399mAh |
Capacity from 4.2V down to 3V @ 5.0A |
1485mAh |
1562mAh |
As it happens, I wasn't happy with these results, and ended up repeating them. The cell that initially had the highest capacity ended up having a lower capacity at the higher discharge rates, despite having the lower internal resistance. This didn't seem right at all. More on this later.
Construction
As can be seen above, the cells have a standard, mid-sized button. This means that using the cells in series should not be an issue, and there should be no problems using the cells in lights that have use physical reverse polarity protection, or have issues with flat top cells for any other reason.
I was having some problems getting my magnets to attach to the button. The magnet was tending to tip over on to the shoulder of the cell, reducing contact with the button, and effecting the internal resistance. The magnet's greater attraction to the shoulder of the cell leads me to conclude that the button is aluminium rather than steel. Nothing wrong with that of course..... it just makes it harder for me!
The negative end uses a 'foil-type' contact - this could lead to wear and tear occurring quicker than with a cell with a metal plate base.
The wrap is a vinyl style heat shrink, rather than the brittle tape type that some cells have.
Light compatibility
Light |
Characteristics |
Fits |
Functions |
Olight M20 |
Wide tube, spring at head, sprung plunger at tail cap |
Yes |
Yes |
SWM T20CS |
Short tube, dual springs |
Yes |
Yes |
Jet IIIM |
Wide tube, tail spring only |
Yes |
Yes |
Fenix TK15 |
Two-piece tube – narrow at head Short tube, short spring at head |
Yes – but snug |
Yes |
Fenix TK11 |
Narrow tube, tail spring only |
No |
N/A |
Eagletac G25C2 |
Wide tube, sprung plunger at head (minimal travel), physical reverse polarity protection |
Yes |
Yes |
Nitecore IFE2 |
Narrow tube, physical reverse Polarity protection |
Yes – but extremely tight |
Yes |
The wider of the two cells was used for this test.
The Nitecore Infilux IFE2 only just accepted this cell width wise, and required the head to be removed so that the cell could be pushed out.
Charger compatibility
Charger |
Fits |
Functions |
4Sevens single bay |
Yes |
Yes |
Trustfire TR-001 |
Yes – but tight |
Yes |
Ultrafire WF-139 |
No (1) |
Yes (1) |
Ultrafire WF-188 |
Yes |
Yes |
HXY-042V2000A |
Yes |
Yes |
XTAR WP2 II |
Yes |
Yes |
Jetbeam/Sysmax Intellicharge i4 |
Yes – but tight |
Yes |
Pila IBC |
Yes | Yes |
(1) The cell will not sit flat in the cradle – the cradle is a fraction too short – but the cell’s positive button still makes contact with the charger’s positive terminal, and charging will proceed.
Internal Resistance
After my initial testing and the odd results it produced, and deciding that this may be related to the poor contact with the positive end magnet, I tried measuring the internal resistance with a crocodile clip holding on to the button via the vent holes. Despite the minimum area of contact this produces, and not being the most stable of contacts anyway, the internal resistance figures did lower in comparison to my initial measurements.
The below table shows the new IR figures, and shows comparisons to other batteries based on the Panasonic NCR18650A cell: -
Cell |
Voltage |
Internal resistance |
Xtar 3100mAh 1 |
3.75V (storage charge) |
101mOhm (crocodile clip) |
Xtar 3100mAh 2 |
3.75V (storage charge) |
104mOhm (crocodile clip) |
AW 3100mAh 1 |
3.96V (as received) |
112mOhm (magnets) |
AW 3100mAh 2 |
3.97V (as received) |
112mOhm (magnets) |
Redilast 3100mAh 1 |
3.63V (as received) |
106mOhm (magnets) |
Redilast 3100mAh 2 |
3.62V (as received) |
106mOhm (magnets) |
Excell 3100mAh 1 |
3.75V (storage charge) |
112mOhm (magnets) |
Excell 3100mAh 2 |
3.75V (storage charge) |
110mOhm (magnets) |
Intl-Outdoor 3100mAh 1 |
3.62V (as received) |
142mOhm (crocodile clip) |
Intl-Outdoor 3100mAh 2 |
3.63V (as received) |
150mOhm (crocodile clip) |
Some of these cells have already seen a little use, some are brand new out of the packet, hence why some are shown as having received a storage charge, and some say 'as received'.
Discharge Cycles
These are the results that I measured after switching to connecting the positive end of the battery to the charger via a crocodile clip. Unfortunately, it is only possible to carry out the discharge from the initial voltage once, so I have carried those over from my original results.
I have carried 0.2C (0.6A) discharges down to 2.5V to measure the true capacity of the cell (0.2C is the discharge capacity that most manufacturers specify), and down to 3V to see what difference there is in capacity. I have then carried out discharges at 1A, 3A and 5A to see how the cells perform at higher rates. That should give an idea of how the cell will perform with moderately driven XR-Es, XP-Es and XP-Gs (1A), fully driven MC-Es, P7s, XM-Ls and moderately driven SST-50s (3A), and with heavily driven XM-Ls and fully driven SST-50s (5A).
I hope to add images of discharge curves at some point - once I work out how to use Logview! I have all the discharge data saved so that I can go back to it at a later date.
|
Cell 1 |
Cell 2 |
Initial voltage |
3.625V |
3.630V |
Quoted length |
68.5mm +/- 0.5 |
|
Quoted width |
18.4mm +/- 0.1 |
|
Measured length |
69.02mm |
69.00mm |
Measured width (max) |
18.68mm |
18.58mm |
Weight |
46.48 grams |
46.37 grams |
Capacity from storage down to 3.00V |
1131mAh |
N/A |
Capacity from storage down to 2.50V |
N/A |
1282mAh |
Internal resistance after storage charge |
101mOhm (crocodile clip) |
104mOhm (crocodile clip) |
Capacity from 4.2V down to 2.5V @ 0.6A |
2956mAh |
2945mAh |
Capacity from 4.2V down to 3V @ 0.6A |
2832mAh |
2810mAh |
Capacity from 4.2V down to 3V @ 1.0A |
2754mAh |
2764mAh |
Capacity from 4.2V down to 3V @ 3.0A |
2448mAh |
2429mAh |
Capacity from 4.2V down to 3V @ 5.0A |
1730mAh |
1722mAh |
Conclusions
After switching my method of connecting the cell to the charger, internal resistance was lowered. While the maximum capacity of the cells dropped in the testing that followed this change, and the extremely close capacity matching at 0.6A down to 2.5V was lost, capacity matching at higher discharge rates tightened up, and the usable capacity at 5A increased. Maximum variation in capacity was 22mAh.
Lesson learnt - find the connection with the lowest resistance prior to testing. This test should have taken half the time it did!
There was around 130mAh increase in capacity when discharging down to 2.5V, but you are still getting over 2800mAh when only discharging down to 3V, so owners of lights that cut out at 3V are loosing little, and still getting a cell with a high capacity. Capacity remains good, at over 2400mAh at 3A. A lot of voltage sag is occurring at 5A, leading to the battery hitting 3V early, and reducing usable capacity as a result.
The cells are rather wide, which could cause issues with some lights, but the button tops ensure no issues with fixed contacts or physical reverse polarity protection - if it fits in your light, it should work. It was possible to charge the cell in all the chargers I had to hand, though it was a tight fit in a couple of cases, and in one case, had to sit in the charger at an angle, though it did still charge.
I would have liked to have seen a solid metal base for longevity, but maybe this would lead to the cell being longer.
All in all though, the Xtar 3100mAh cells performed very well, providing a high capacity for low and medium power lights. High powered lights would have reduced run times due to the voltage sag that these cells suffered from.