(Speaking of LED bulbs, I recently bought some 1600 lumen Philips LED bulbs, they provide a fabulous, even, illumination for about €3 each. When they are turned on, very impressive how bright the room is)
Anyway what I’ve got for you today are what I think will eventually become the next generation of rechargeable batteries. They have identical form factor to standard batteries so you can stick them in anywhere. Unlike NiMH rechargeables which have a cell voltage of 1.2v (which makes things noticeably dimmer than if you use 1.5v non-rechargeables), these provide a constant 1.5v. By constant, I really do mean constant: they output exactly 1.5v from full until empty, whereupon they then go to 0v. This constant voltage has some big advantages, mainly that things remain bright and never dim over time, like you especially get with any other kind of battery.
The way these batteries work is that they have a lithium ion cell, which like all lithium ion cells outputs about 3v. A very small embedded computer runs a DC-DC voltage converter to downgrade the current voltage (about 3.6v full, down to about 2.5v empty) to 1.5v. This is why the voltage is completely constant until the battery is empty. Essentially, the little embedded computer ‘simulates’ a real AA battery.
Furthermore, because each battery is a small computer, you can recharge them using standard micro USB. The embedded computer takes in the 5v from the USB and charges the lithium ion cell, changing the colour of a little LED from red to green once full. You can only really get these next generation rechargeable batteries in the West from Amazon, where they are sold under the Blackube branding, amongst others. As you will see, they cost about €40 for four AA batteries on Amazon, which is very pricey.
Blackube and all the others are an OEM rebrand of Chinese manufactured batteries. One of the biggest of the original manufacturers is ZNTER, and you can acquire what appear to be the exact same batteries as the vendors on Amazon are selling directly from China for about half the price, if you are willing to wait six weeks or so. Mine arrived last week, and here is what they look like:
The first thing you notice is how light they are, much lighter than alkalines, probably about that of zinc chloride batteries. The second thing you notice is the micro USB slot, which is on the top for the AA batteries, and on the top’s side for the AAA batteries. Other than those two differences, they look every bit exactly like AA or AAA batteries. Plugging them into something, the voltmeter reads a rock steady 1.55v at 200 mA discharge, and 1.53v at 500 mA discharge. Here are the characteristics for the AA size as according to various sources:
|Alkaline non-rechargeable (source)||NiMH rechargeable (source)||ZNTER manufacturer claim (source)||Blackube claim (source)||Blackube measured by lygte (source)|
|Capacity @ 0.1A discharge||2.5Ah||2.0Ah||1.7Ah||1.7Ah||1.65Ah|
|Median voltage @ 0.1A discharge||1.2v||1.27v||1.5v||1.5v||1.5v|
|Power @ 0.1A discharge||3.0Wh||2.5Wh||2.59Wh||2.55Wh||2.47Wh|
|Runtime @ 0.1A discharge||25h||21h||17h (est)||17h (est)||17h|
|Max charge cycles||n/a||1000||3000||1000||n/a|
|Capacity @ 1.0A discharge||1.21Ah||2.0Ah||n/a||n/a||1.59Ah|
|Median voltage @ 1.0A discharge||1.05v||1.25v||n/a||n/a||1.5v|
|Power @ 1.0A discharge||1.3Wh||2.54Wh||n/a||n/a||2.36Wh|
|Runtime @ 1.0A discharge||1.2h||2.0h||n/a||n/a||1.6h|
As usual, you should not trust Chinese manufacturer claims. They are way off reality. Even the Blackube claims are slightly short of measured reality. As you can see, if my ZNTER batteries actually match the Blackube batteries, they are competitive with Alkaline and NiMH at low current draws, though with 20%-33% shorter runtime in exchange for maximum brightness. At higher current draws, these batteries remain competitive with NiMH, and blow away Alkaline batteries which do not cope well with high current draws. They still retain a 20% runtime deficit, but again you get 1.5v throughout.
Now I don’t know if the batteries I bought are in fact identical to the Blackube ones yet. I don’t have the equipment here to test them (the constant voltage confuses all my NiMH assuming equipment), so all I can report right now is anecdotal experience.
Certainly they do work. I have a set in some Christmas lights currently. You’d typically get about five days if you put NiMH into them, but the lights get dull quite quickly. Putting these ZNTER batteries into them they are very bright throughout, but for maybe a little less than three days. One very curious thing is what happens when one of the three batteries in those lights runs out – it ‘vampires’ 0.5v from the remaining two batteries, so 2.5v reaches the lights instead of the expected 3.0v. This means that in practice, the lights are very bright until they go quite dim, as 4.5v drops suddenly to 2.0v. You then don’t know which of the three batteries is empty, so you must recharge all three. Charging does take under two hours, but they draw 0.5A each at the beginning of the charge, not the 0.4A reported by lygte, and definitely not the 0.35A claimed by Blackube. As they approach full, they taper back current heavily, and they never get more than mildly warm around the USB socket (where the IC is).
From this anecdata, I’m thinking that despite the identical outward appearance of these ZNTER batteries to the Blackube ones, they are probably not the same, and not in favour of the ZNTER ones. They did cost half as much, and I definitely don’t think they are half as good, so on that basis I’ve done well.
As I really want to find out the true characteristics of these batteries before I put them into regular use (particularly if they might catch fire under load), I have ordered a cheap programmable load tester from China. Once it arrives I’ll be able to drive a 0.1A and 1.0A load upon them, and see how well they perform.
Until then, I will conclude by saying that these next generation batteries aren’t quite there yet as an Alkaline or NiMH battery killer. But they continue to experience rapid improvement year on year, even just two years ago claimed capacities were considerably less, and as miniaturisation of the components allowing more lithium in the same form factor progresses, that will continue. I would not be surprised if three years from now that this kind of rechargeable battery won’t be superior to NiMH on every metric except price i.e. they will last just as long in runtime at both low and high currents, but output 1.5v throughout, and have thrice longer recharge lifespans. Right now four AA batteries can be got from China for about €13, about double what Amazon charges for their very good NiMH rechargeables. I certainly can see that gap closing to under 50%.
I don’t foresee these batteries ever beating alkaline for long lived low power applications. If you need to power a wall clock for years, expensive alkaline batteries can deliver more than 3.5Wh over five years or more. That cannot be beaten by anything containing an embedded computer which needs to draw some power, no matter how little, never mind the fact that rechargeable chemistry cannot avoid much higher self discharge rates than non-rechargeable. However for applications with very high current draw where even high quality NiMH experiences considerable voltage sag, this kind of rechargeable battery will dominate as lithium ion can deliver vastly more watts than NiMH ever could.
I’ll make another post here with empirical testing of my new batteries when my test equipment arrives. If that doesn’t happen until after Christmas, Merry Christmas!
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