Intro #
I always measure the batteries I buy because they often do not hold the parameters rated by the manufacturer. It is also interesting to know the parameters at the first use to see how they degrade over time. This page will list those measurements and my opinion about the batteries I get. I try buying more than one battery of a type to make sure it’s not a lemon but it is not always possible or practical and even if I do, I have no way to make sure they are not from the same batch and thus share the same problems so please keep that in mind.
I measure the parameters that are most interesting from my perspective:
- Voltage at delivery - just to make sure the battery was not stressed by non-optimal storage voltage. The ideal voltage should be between 3.7V-3.9V per cell.
- Real capacity - there are multiple ways of measuring that but here I present the value I get when charging the battery from 3.2V to 4.2V at 1C. Due to great Lithium batteries efficiency, I found this value to be the same (or just slightly larger) as the one I get when I discharge the battery at ~1C and I expect the battery to have its rated capacity at 1C discharge. It is just more practical for me to measure when charging, not discharging.
- Internal resistance after fully charged the battery, measured at 1Ω load for the whole pack. Great, high current Lipos have 3-6 mΩ per cell but I consider anything below 20mΩ to be good and up to 25mΩ is OK. The higher the C rating, the lower the IR should be but in practices this is not always the case.
Having those measurements, and the rated values, we can calculate:
- Capacity ratio - the percentage of the real capacity to rated capacity. I expect this to be close to 100%
- Nominal current - the current that the battery is rated for, based on rated capacity and rated C
- Vdrop at nominal - the voltage drop we get at Nominal current
- Vdrop in percentage - the ratio fo Vdrop at nominal current to a nominal voltage of Lithium batteries (3.7V per cell). My experiments show that good batteries (properly C-rated) have this value around 15%.
- Max current - this one is tricky as its just my definition of the maximal current. I calculate the current needed for the battery to drop from nominal 3.7V per cell to 3V per cell given the IR of fully charged battery. I use this together with Vdrop in percentage to evaluate the C-rating of the battery.
Electroriver 1100mAh 2S 20C #
About the battery #
This is the cheapest battery from this family I found and one of the cheapest Lipo batteries I could find on Polish shops overall. All of the Electroriver batteries share the same manufacturers description, which claim they have:
- Subzero Power™ - better efficiency at low temperature,
- Nanosafe™ system - which minimizes the risk of fire in case of physical damage,
- 20% better lifetime (in cycles) compared to other Lipo batteries
- Minimal internal resistance
Measurements #
| Battery No. | Voltage at delivery [V] | Real capacity [mAh] | IR when full [mΩ] | IR per cell [mΩ] |
|---|---|---|---|---|
| 1 | 3.83 + 3.83 | 785 | 60.85 | 30.43 |
| 2 | 3.83 + 3.83 | 784 | 64.82 | 32.41 |
| 3 | 3.83 + 3.83 | 807 | 57.57 | 28.76 |
| AVERAGE | 3.83 + 3.83 | 792 | 61.08 | 30.52 |
Calculations on average values:
| Rated capacity [mOhm] | Real capacity [mOhm] | Capacity ratio [%] | C-rating | Nominal current [A] | IR [mΩ] | Vdrop at nominal [V / %] | Max current [A] |
|---|---|---|---|---|---|---|---|
| 1100 | 792 | 72 | 20 | 22 | 61.08 | 1.34 / 18.1 | 22.97 |
Verdict #
The battery real capacity is its biggest disappointment - it’s only around 72% of the rated capacity. I know its a cheap battery but it’s not an excuse for me. When I buy 1 liter of water, I expect it to have no less than, say, 0.95l, no matter how cheap it is. Since the voltage drop at nominal current is around 18%, I would say the C-rating isn’t overly exaggerated, especially since the rated current is 22A while the calculated max current is almost the same at 22.97A. If you take a closer look at the photo, you will find, however, that while the label on the battery itself claim 20C, the label on the package is 25C which is inconsistent. Fortunately the one on battery seems to be closer to the truth.
I can’t check neither Subzero Power™ nor Nanosafe™ technologies but since both internal resistance is not only nothing special but is pretty high compared to my other batteries and even such a basic parameter as capacity is highly inaccurate, I have trouble believing other claims of the manufacturer. As usual, the devil is in the details and I suspect their claims are compared to the batteries with other chemistry so they just have the same properties as all Lipo batteries, nothing more.
I had 3 of those and they all had similar parameters so its not a matter of a lemon. I did get all of them from one supplier so they may be from the same batch.
GFC 1000mAh 2S 30C #
About the battery #
This is yet another very cheap 2 cell battery, only slightly more expensive than the Electroriver 1100mAh reviewed above. While you can see Deans plugs on the photo, it originally comes with mini-tamiya. I got two of them for measurements.
Measurements #
| Battery No. | Voltage at delivery [V] | Real capacity [mAh] | IR when full [mΩ] | IR per cell [mΩ] |
|---|---|---|---|---|
| 1 | 3.83 + 3.83 | 883 | 36.84 | 18.42 |
| 2 | 3.83 + 3.83 | 899 | 36.75 | 18.38 |
| AVERAGE | 3.83 + 3.83 | 891 | 36.79 | 18.40 |
Calculations on average values:
| Rated capacity [mOhm] | Real capacity [mOhm] | Capacity ratio [%] | C-rating | Nominal current [A] | IR [mΩ] | Vdrop at nominal [V / %] | Max current [A] |
|---|---|---|---|---|---|---|---|
| 1000 | 891 | 89 | 30 | 30 | 36.79 | 1.10 / 14.86 | 38.05 |
Verdict #
Although the battery capacity is not as advertised, it is only 11% short which is not that bad compared to Electroriver one with 28% short. Apart from that, the battery really has nice properties - the internal resistance is quite decent for such a small battery at around 18mΩ per cell. With 30C at rated capacity, the rated current is 30A and the Vdrop at this current is also quite nice, with only 14.86%. The Max current exceeds the nominal current quite significantly as well so the C-rating definitely isn’t made up. So even though it is so small, you should be able to use it even for fairly high power guns.
If only the capacity would be real, I would have no complains for this battery. But if you just scratch out the 1000mAh and threat this battery as it was 900mAh, you can think of it as a very solid one! And it still have more capacity than the Electroriver that was rated for 1100mAh..