Mini-Review for the Tenergy Centura 9V and TN141 (2-bay) charger
Since a good number of DMM uses 9V battery, I am sure I am not alone in thinking of using a recharge battery. I have two main reasons to choose a recharge: (1) When data logging, I want to make sure that the battery goes the distance. Inserting fresh primary battery each time is costly. (2) Corrosion - on a few occasions, I forgot to turn off the equipment. A half dozen times or so, even “quality batteries” like Duracell leaked on me and make a mess inside the equipment. With NiMH, I may “drove it negative” and damaged the battery, but I have yet to have one of them leak on me when I left the equipment on for weeks.
Selection for 9v LSD (low self-discharge) NiMH is limited. With some apprehension I selected the Tenergy Centura. I read in a review someone complained that his Centura does not fit his guitar. So, with apprehension, I ordered a couple of Centura 9V and the TN141 charger. Below is a mini-review of the batteries and the charger.
The Centura 9V LSD Battery
Prefix:
First, let me address the “does it fit” aspect. Yes, it fits the UT61E but it is a squeeze. The Centura is a 7-cell battery verses the typical 6-cell 9V battery. Consequently, it needs more space for the extra cell. It gets the extra space by making the body taller and the power-connecter buttons a bit shorter. The total height is exactly the same as other 9V batteries. From the attached photo, you see that the body is about 1.5mm taller and the buttons are shorter by an equal amount. The UT61E compartment has a separation between the buttons and the battery body, but the body-side of the compartment has enough room to squeeze in the extra 1.5mm, and the shorter buttons still stick out enough for a good electrical contact. It fits the snap-on power connectors just fine, so if that is what you DMM/equipment uses, you have no worry here.
About the battery:
The Centura 9V LSD nominal spec is 8.4V, 200mAH when discharged at 40mA to 7V with a claimed “over 1000 charge cycle” life span. Tenergy website did not post any numbers for charge-retaining over time, but I have seen sellers’ web posting at 12 months - 85%, and I have read reviews on it retaining merely in the 65% range in 12 months. This mini-review does not contain any charge retention test.
Both batteries from the two-pack appear fairly well constructed with one exception: the clear plastic covering were not shrunk as far as it should. You can see some spots where the plastic wrapping has slack wrinkles. Apart from this small detail, the batteries look and feel very well constructed. They look solid and well made. (They are made in China)
Unlike many 9V recharge batteries with 6 cells, the Centura is a 7-cell NiMH. So it delivers 8.4V nominal instead of 7.6V for the 6-cell batteries. They claim that with 8.4V nominal, it can deliver more useful power as more power can be delivered before the cut-off voltage for whatever it is powering.
The Tests:
I did the same tests on both batteries each with 5 discharge (and charge) cycles. First the initial fast discharge with the batteries as received (without topping up), then I did two “fast and slow” cycles of first fast discharge then recharge and do a slow discharge. That is 5 discharges for each battery. The batteries were discharged to just below 7V and then recharged for the next run.
The fast discharge was done at just over 1/3C (~60-80mA) with a 119ohm dumb resistor. The slow discharge was done at around 1/10C (~20mA) with a 440ohm dumb resistor. Since the load is a dumb resistor, the current varied with the voltage.
Battery 1
1. Fast Initial: 134mAH (1115mWH), Duration=1:55
2. Fast Discharge: 203mAH (1735mWH), Duration =2:49
3. Slow Discharge: 214mAH (1855mWH), Duration=10:52
4. Fast Discharge: 210mAH (1806mWH), Duration=2:55
5. Slow Discharge: 215mAH (1884mWH), Duration=10:48
Battery 2
1. Fast Initial: 140mAH (1159mWH), Duration=2:01
2. Fast Discharge: 204mAH (1735mWH), Duration =2:52
3. Slow Discharge: 208mAH (1803mWH), Duration=10:52
4. Fast Discharge: 203mAH (1726mWH), Duration=2:51
5. Slow Discharge: 215mAH (1877mWH), Duration=10:48
The discharge curves are attached.
As the number shows, both batteries arrived with about 70% full. After the first full charge, they meet and slightly exceeded the spec (spec is 200mAH at 1/5C – even at 1/3C, the numbers are 203 and 204mAH). When discharged at 1/10C, it is well above 200mAH at 210mAH and 215mAH.
The Centura(s) perform to spec and exceeded it (slightly). They claim that with 8.4V nominal, it can deliver more useful power. My tests show at 1/10C discharge, 94%-96% of the energy were delivered before it dropped below 8V (see attached graph). I did not do a complete graph for the higher 1/3C discharge. I did the calculation for one of the four 1/3C discharge: 92% of the energy was delivered before it drops below 8V.
Thus far, I am pleased with the batteries. The UT61E drains at around 5mA. Now I know if I top up the battery, I can have a 40 hour run. This is much less than the 400-500mAH typical primary cell delivers; but when a battery is already in use, I can never be sure how much of that 500mAH is actually there and fresh battery every run is expensive.
The draw back:
Discharging a rechargeable battery to well below 1V per cell is not a good idea. It will damage the battery in the long run. The UT-61E low battery warning is around 5V. Given the low drain (5mA) of the UT61E, I am not sure how quickly it will drop the battery from 7V to 5V. So the battery may be held at below 1V per cell for a lengthy period of time waiting for the low battery warning to come on. I cannot test this without potentially damaging the battery. With an enclosed battery compartment as the 61E is, checking the battery voltage is inconvenient.
The TN141 charger
The charger is very small with a flip out plug. It measures merely 85mm by 65mm wide chopped-off-oval shape and about 25mm high. It is a 2-bay charger at 100mA charge rate. The two bays are independent each delivering 100mA. The termination method is “negative-delta-V” with a 5 hrs safety timer. It has reverse polarity detection, short circuit, and bad battery detection.
Each bay is equipped with a multi-color LED. RED means charging, GREEN means done charging. When it detects reverse polarity, short circuit, or bad-battery, it will blink RED. I have seen it on AMBER and I am not sure what it means (more on this later).
Testing the charger:
The charging is uneventful and worked well. With it being so uneventful, I decided to charge a full battery. The RED turn GREEN in a few minutes reassuring me that the NDV termination is working properly.
Pulsing charge:
In fact, the charger exceeded expectation. At the low price of under $10 including shipping, I was expecting a dumb-smart linear charger. It actually is a pulse-charger. It pulses at 250mA once every 2 seconds (or so) averaging 100mA. Once fully charged, the pulse drops to about once every 10 seconds to maintain the charge. I have not left the battery on it long enough to say if there is cut off time.
Gone milli-volt or Driven Negative:
To test how it behaves with a marginal cell, I use 6AA to simulate a 9V battery. I have a 4 AA cells that “gone milli-volt” each sitting at under 100mV; another 2 AA cells that were driven negative. I set them up in a series to simulate a single typical 6-cell 9V battery. Together, the pack measures at about 200mV.
The TN141 started with a 3mA steady current. After it got the pack up to around 6V, it switched over to pulse the 3mA. At around 8V, it switched over to normal charging of 250mA pulse every two seconds. I did not expect the pack to fully charge with a single run as the capacity well exceeded 500mAH. The safety timer would stopped the first charge run at around 500mAH (5 hours). But during the testing, it was restarted a number of times to test the voltage. The pack eventually charge fully.
When a 6-cell/7-cell battery gone negative, there is not much point in trying to revive a battery. With one or two cells sitting negative, the battery probably can’t hold much charge or deliver much punch. The cell is likely too damaged to use. But this test shown one can easily jump-start the battery from negative to milli-volt and the TN141 will take it the rest of the way. Once it is fully charged, one can then tests the battery to see if it is worth keeping.
LED on AMBER:
I noticed during one of my test cycles, my battery#2 shown an amber/orange light upon completion just prior to dinner. Since dinner was waiting, I could not do much checking aside from measuring the voltage which was at a typical voltage for a full (or almost full) battery straight off the charger. After dinner, I used the battery a bit and it all seemed normal. I recharged it and the LED was GREEN.
During that AMBER cycle, I was also doing something else and used an extra wall-wart. The TN141 was sitting directly on that wall-wart and that wart was running fairly hot. I am not sure that was affecting the charger. In any event, I have not been able to reproduce the AMBER light.
Conclusion:
So far, I am happy with the Centura(s) and the charger. Unlike many other Chinese made batteries with exaggerated claims, the Centura’s actually exceeded spec. The charger worked fast and worked well. I will monitor these for long-term performance and update if anything interesting happens.
Home
Help
Search
Login
Register
