New Part Day: SMD Batteries

Here’s a tip for all you retrocomputing enthusiasts or even anyone with an old computer in the garage. Go remove the battery. Yes, that old mid-90s desktop has a battery inside for the real-time clock, and it’s a ticking time bomb. Batteries leak, and they’ll spew goo all over the circuit board, irreparably damaging your piece of electronic nostalgia. This goes for all electronics, too: that badge collection is going to be a pile of broken fiberglass in a decade. Remove your batteries now.

While lithium cells soldered to a motherboard will leak, now there might be a new technology that will allow our modern electronics to last for decades. It’s a solid state battery. The FDK Corporation is now handing out samples of a battery that looks like a large SMD cap. They come on tape and reel, and they’ll never leak.

Thanks to massive investments in battery research, batteries are getting more power-dense, and form factors are getting weird. Your AirPods need a battery somewhere, and manufacturers are figuring out the best way to put a battery into something that can be assembled by a pick and place machine. This battery is the answer to these problems, packing a 3.0 V, 140 μAh lithium cobalt pyrophosphate cell into a package that is just 4 mm by 2 mm by 2 mm. It’s a battery that looks a surface mount component, and it’s installed the same way: this is a pick-and-placeable battery.

While the capacity of this battery is tiny — a 1225 coin cell has a capacity of about 50 mAh, and this battery has a capacity of 140 μAh, three whole orders of magnitude smaller — sometimes that’s all you need. If you need a battery for a RTC, this SMD battery will work.

60 thoughts on “New Part Day: SMD Batteries

  1. Very interesting! I’d never even thought about solid-state batteries.
    (Minor nitpick: are you sure you didn’t mean “Thanks to massive investments in battery research, batteries are getting more energy-dense”? Energy density is the main problem with rechargeable cells, not power density.)

  2. “and they’ll never leak”

    It will take more than just a statement like this, to make me get over my trauma of having seen all those beautiful vintage computers that have been destroyed by the evil leaking Varta.

    Just one consolement: these modern computers will never be ‘vintage’. Just ‘old, useless and unwanted’. So nobody cares much anymore about batteries that start leaking after 15 years.

    1. Nostalgia is in the eye of the beholder.
      The new crop of retro aesthetic games all have blocky lowres textures and sharp low polygon models because Playstation and Quake. As an examples see “Strafe” & “Paratropic”
      In 10 or 15 years the Retro games are all going to feature slow texture loading, shitty LoD pop-in, and jumpscare villains that teabag your corpse.

      1. The irony is that pixel art never looked like pixel art because it was designed to make use of the quirks of CRTs to effect what can be described as “sub-pixel” rendering.

        It looked much better originally than the blocky mess that passes off as “retro games” these days.

  3. A mid 90ies RTC probably uses quite a substantial amount of current to stay on time, compared to more modern RTC solutions. So, maybe the very tiny solid state battery really fits todays needs as a time-keeper. One of the lowest power RTCs i know needs around 40-50nA, so it should at least keep your time going for a few months, even from that tiny 140µAh battery.

    1. I’m not sure that that’s completely correct. A mid-’90’s RTC would have been a separate chip, optimised for low power. Today’s RTC in a typical computer is built-in to a SoC or a Northbridge, both made on a process optimised for speed.

      One can still buy dedicated RTCs with I2C or SPI connections to the world. Their datasheets suggest they draw about the same amount of power as ones from two decades ago. (I suspect they are still made on a similar process.)

      1. BTW, my favourite RTC chip that I design into all my products is at least 15 years old. I use that particular one because it has a special feature that more recent RTCs don’t have.

    2. A mid 80’s RTC (read: digital wristwatch) would easily last several years on mid 80’s tiny coincells.The early CMOS technology was super low current (and low speed).. It only started leaking once technology was shrinked from multi-microns to few nanometers.

    1. i don’t think so, they would have mentioned it.
      however, by searching for infos on this part, i also found the TDK CeraCharge.
      It’s also SMD, but rechargeable, and also with a solid ceramic electrolyte.
      EIA 1812 package (4.5 mm x 3.2 mm x 1.1 mm)
      100 µAh at a rated voltage of 1.4 V
      (TDK claims the world’s first rechargeable solid-state SMD battery with this. (October, 30. 2018) )

  4. “While the capacity of this battery is tiny — a 1225 coin cell has a capacity of about 50 mAh, and this battery has a capacity of 140 μAh, three whole orders of magnitude smaller — sometimes that’s all you need. If you need a battery for a RTC, this SMD battery will work.”

    Ok, lets assume the use case for an ultra low power RTC such as the AB1815. It even includes 256bytes of backup ram. The power consumption depends on the operating mode:

    XTAL: 55nA, ±2ppm accuracy
    RC + autocal: 22nA, ±16ppm accuracy
    RC: 14nA

    This would yield a theoretical run time of:

    XTAL: 106 days
    RC + cal: 265 days
    RC: 416 day

    “While lithium cells soldered to a motherboard will leak, now there might be a new technology that will allow our modern electronics to last for decades.”

    The RTC used for the calculation is one of the best parts out there (typical RTCs in MCUs take 500nA or more), it only runs for slightly longer than a year. Not for a decade and especially not for decades. And this does not even account for self-discharge.

    So let’s assume the device is a) mains powered or b) has a secundary cell in it.

    a) If it is mains powered, it can be assumed the power outage is repeaded and for brief periodes only. Using a supercap or a larger sized ceramic is a better choice in most cases and doesn’t have an expiery date at all. Or ther might be just enough space to use a CRXXXX battery, wich only cost cents in quantity anyway, and use a cheaper RTC.

    b) If there is a secundary cell, such as a LiPo, it is NEVER drained completly anyway, because it would destroy it. However even if an undervoltage condition is detected and the protection circuit turns off the load, the protection circuit consumes a “hibernate”/ leackage current of 100nA typ. This makes it safe to assume one could safely power an RTC like the AB1815, too.

    So what ARE use cases? The only application I can think of are devices, that have a user replaceable battery that needs to be replace fairly often and the RTC must not stop even if batteries are removed for a few days. Or farting novelty gadgets, which are build to be discarded quickly anyway. So in the end they might be perfectly suited for the badge madness makers seem to love that much.

    Dear hackerday team,
    please do some back-of-the-envelope calculations before writing highly praising articals like these.
    Thanks.

    1. You forget that you’re not limited to using just one. These are meant to be jellybean parts – have two, have ten if you like – they come in a roll.

      The point is that you don’t need any special battery holders – the battery can be integrated on the same board in the same process as the rest of the circuit, eliminating a bunch of handling steps and costs, and it scales up and down according to need.

      1. Nah, the point of a battery the size of a Rice Krispie is obviously the size. Nobody would use dozens of these to replace a watch battery. The economics would be terrible, that’s the economics of all batteries, you buy them in the size you need. I’m not sure exactly how they currently mount batteries to boards, but it can’t be so difficult as to make buying dozens of these economical. The cost of making a battery is much more than that of mounting it.

        1. Yes they would, because it means they can skip the extra step of installing the battery clip and the battery. It’s a non user-serviceable part anyhow. The economy of these is one-size-fits-all because with batteries you need to make dozens of different sizes for various needs, whereas this you only need to make in one size, which makes it cheaper.

  5. A coin cell for a RTC usually works for 10 years,
    50 / 0.2 = 250 (50 mA for coin cell and i use 200 micro amper for the smd one, so more than the real one)
    3650 (days in 10 years) / 250 = 14 days

    maybe some charge will be loose for the aging… but I doubt that will work fine as battery for a RTC for more than 2 months…

    To be more sure need to search more data about how much will consume a RTC circuit in old computer

  6. So basically, we just have to wait for a fellow hacker to create a piece of hardware who can replace a coin battery without unsoldering anything on our precious retro hardware ? Can’t wait to see it :)

  7. Now, this is interesting , imagine spread your battery around the dead space on your pcb , or maybe on the bottom layer.
    I don’t think the idea is to use one of them , but more in parallel

  8. If you have an old original Xbox laying around, v1.5 or earlier (non 5838 BIOS), you should open it up and remove the clock supercapacitor in there right now. They are beginning to leak acid which can severely damage the board. The only downside to removing it is that the clock needs to be set every time you disconnect to mains. If you have an old softmod or BIOS, you should install a newer one to compensate for a clock boot loop that could happen.

  9. While I’m excited for the hacking possibilities right now, I have to admit I’m also kinda weary of this. This has the potential to really change how boards are designed. And when the batteries die (or, in the case of rechargeable batteries which these appear to be, have gone through enough charge/discharge cycles that they lose their ability to hold a charge), they are going to be much harder to replace than current batteries are.

    I guess I’m not thrilled to see hardware become harder to hack instead of easier. I suppose this isn’t the only trend in hardware that is moving this way, though…

  10. What usually leaks are the NiCd batteries and the 1/2 AA lithium cells as used in old Macs (and if those leak it gets REALLY ugly). I also see some SMD electrolytic caps leak and damage boards (See Amiga 600, 1200, 4000, CD32 for example).

    On the other hand, so far I didn’t have a single leaking CRxxxx coin cell. They were just dead, but otherwise intact. So I would not hesitate to use a CRxxxx cell in new designs as well since with them I can be sure that the circuit they power will run for years. These SMD cells on the other hand strike me as too low in capacity to be really useful.

  11. 2mm x 4mm = 8mm^2 per battery.
    An average business card is 85mm x 55mm = 4,675mm^2
    Theorically, you could fit 584 batteries on top of a business card, yielding either 81.76 mA or 1,752 Volts, which is enough to build a very compact Cardiac Defibrillator.

    This thing could become the “Next EpiPen”

  12. People keep calling these batteries “solid state”, when in fact they have a solid electrolyte. The positive and negative electrode materials (like the graphite and the pyrophosphate) both undergo non- negligible volume changes from charged to discharged. Not as bad in small batteries, but more noticeable in larger ones, possibly leading to cracks and failure of the electrolyte.

    Solid state is electrons and holes, not ions

    /pedantic electrochemistry

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