I need to find a rechargeable micro battery solution.

Hi everyone!

First off, thanks for taking the time to give this a read. The last few places I tried asking didn't really have much to offer in return, lets hope things will be different this time around! I'm not properly educated when it comes to this level of technology so I'm making more assumptions than I am informed decisions at this point, and that needs to stop if I want to get anywhere positive with this project.

I'm working on a small device which currently has a footprint of roughly 1"w x 1"d x 1/4"h. We were previously stacking two of these to power the device internally, but I want to evolve things a bit. I'm trying to find a power source that is as close in size as possible to the one I linked, as well as being rechargeable. Ultimately I want to be able to recharge the device via a wall/car/USB adapter, and have it shut off the charge current when the batteries are topped off, and switch to AC power. Basically how your typical smartphone works. I know this is a relatively simple task, but I'm attempting to do it in a very small space (the current batteries take up about 20x20x3mm) so I know I'll have to get pretty creative.. any help is appreciated, I can't disclose too much about what I'm working on but I'd be happy to try to answer any questions you guys might have.

I received a couple replies on another board that I feel are relevant enough to share with you here:

Them said:

How much power do you need? What kind of discharge characteristics can you deal with?
There are rechargeable CR2016 batteries.
Am I right in understanding that you need to fit the recharging circuitry within the space as well?! That might be a bit tough, but you can probably use a FET(s?) to switch between battery/external power, and have the charging controller external to the device (built in to the charger).

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Me said:

Forgive me in advance if my answers to your questions seem noobish, I'm trying to take something I have only basic knowledge of and make it better, so bear with me.
I need enough power to keep a single LED bulb lit (whether that be solid, blinking, fading, etc) for at least 4-6hrs, but the longer the better. 12 would be fantastic, 24+ would be incredible (although probably unrealistic), etc.
I wasn't aware of that, hadn't come across any in my searches so far. That might make things more simple! I did come across this earlier, it's definitely a different size to deal with but given the specs I would think if I could make it fit, it might be worth it to try?

As for charging, that sounds like a grand plan. What are your thoughts on the hardware side of charging something like this? I'd ideally like to have it all internal, (again, like a cell phone), so that you can plug in an external cord. The plug type doesn't matter honestly, could be MicroUSB for all I care, just so long as when the device is done charging you can pop it off the cord and you'd never know there was a charge port unless you looked. Having the charging controller on the charger itself sounds like a great idea too, the more hardware we can keep off the device itself, the better!

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Them said:

If it's only an LED you need to power, and the LED only needs to be an indicator light, you may want to investigate supercapacitors (sometimes sold as 'ultracapacitors').
Advantages: Small, very easy to charge, charges very quickly. Disadvantages: Far lower energy density than a real battery.
You may be able to keep an indicator going for 6 hours using the charge from a supercapacitor which is the size of a stack of coin cells if you make a low-wattage LED blink at low frequency / low duty cycle. If people need to instantly recognize that the LED is on, then this might be a problem. If we're talking about something more like a smoke detector, where you can expect people to be able to stare at it for five seconds to wait for an LED blink, then it's probably quite possible.

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Me said:

I don't think that would work, we need these lights to be very bright. Not blinding, but close. Also, some fade from color to color, some blink rapidly, etc.. so the power usage would probably be too much for a super/ultracapacitor. I could be wrong though.. in comparison, using the 2 CR2016's we get anywhere from 2-4hrs+, depending. So, as long as we don't go under that, we're golden.

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Thanks in advance for any help you may have to offer, I could really use some guidance here haha.

how many LEDs and what size? 5mm take 20mA and can range up to 40,000 millicandela
We need to know the load. But for cost, it's hard to beat CR2016's for price and size.

**broken link removed** Lithium-manganese dioxide Lithium-carbon monofluoride
IEC name CR2032
ANSI/NEDA name 5004LC
Typical capacity 225 mAh = 10 mA for 22 hr
Nominal voltage 3.0 V
YOu might be better off with 2054
THese are expensive but the best
https://www.panasonic.com/industrial/includes/pdf/Panasonic_Lithium_BR3032.pdf

Just a single 5 mm (T-1 3/4) bulb. As I stated above, we're dealing with up to 7 colors per bulb with several hand-fulls of different possible settings (strobe/blink/solid/etc) I'm not sure exactly how drastic of an effect that has on battery life but I figure it's worth mentioning.

Say I wanted to run this at full power using this as it's power source, what kind of performance/battery life should I expect? And, how would I go about wiring the battery & LED up so that I could power the LED via battery, or (if the battery is charging or at full charge & plugged into power source) AC current, like how a smartphone/laptop works?

Also, I forgot to mention, my ultimate goal is to be able to charge roughly a dozen of these devices off of a single harness. So, essentially it'd be one wall adapter running out to 12~ individual connectors. Where should I start with something like that?