Everything mankind has done has but one purpose. Make babies and live. That is priority numero uno. We need stuff to live, we need stuff to live better, getting stuff causes damage. Deal with it. If you want a better life it comes at a cost. Everything costs, find the least worse way to get a better life and stop being a wuss. Do you want electric cars or not? Go research how to make a better battery and get rich, or shut up whining and wait for someone else to make you feel all warm and comfy. Uno Lithium Battery
4 Ways to Power Your Arduino:
USB cable
External power supply, or battery, going into the 2.1mm x 5.5mm DC power jack (recommended 7~12V input)
External power supply, or battery, going into the "VIN" and "GND" pins on the board, via jumpers (recommended 7~12V input)
External, regulated 5V power going straight into the "5V" and "GND" pins; this can even come from another Arduino's 5V and GND pins.
I would look into getting one of those Lithium-Ion cell packs that put out a nominal 7.2V and connecting that to the DC power jack - companies like Tenergy make reputable ones.
Check the power requirements of your Arduino project against the power capacity of the cell packs to work out roughly how much run time you can expect when using them to power it.
Standard Engineer’s response: It depends!
A single Lithium-Ion battery’s terminal voltage will range from 4.2V fully charged, down to as low as 2.7V completely flat, but commonly no lower than 3.0V - it depends on the specs of the cell, and of the Cell Protection Module that’s part of the cell (guards against operating at too low or high a voltage, or drawing too much current).
Automatically that tells us that we need to pay attention to the Vcc supply voltage that the microcontroller (and everything else on the Arduino Uno) will reliably run at.
The key issue here is, What speed (MHz) do you want/need to run the Arduino at? Because you can’t run the Arduino’s microcontroller at max MHz all the way down to minimum Vcc. That ATmega328P on an Arduino Uno has a ‘Safe Operating Area’ of what speed in MHz it can run at, at various Vcc supply voltages:
That’s from page-303 of the ATmega328/328P (and its sisters 168A/168PA, 88A/88PA, and 48A/48PA), all 650 pages of it.
So if you supply the Arduino Uno with >4.5V, you’re good all the way up to 20Mhz! (The Uno happens to be designed with a 16MHz crystal).
But if your Vcc is provided directly from the Lithium-Ion battery (i.e. with nothing more than a Lithium-Ion battery connected to Vcc, no voltage regulator, you put the battery +ve into the +5V pin of the Power-Header of the Arduino Uno), then it could go as low as 2.7V. At 2.7V, the ‘328P is only guaranteed to work reliably if you clock it at 10MHz! Admittedly this is a -40 to +85ºC rating. At ‘room temperature’, you just might be able to run at a higher MHz even at that low 2.7V Vcc.
So you’ve got two choices!
Configure the clock pre-scale register so that your Uno runs all the time at 10MHz, and thus be guaranteed to have trouble-free operation even as your single Li-Ion battery gets all the way down to flat, or…
You need a boost switch-mode regulator that can take the Li-Ion battery’s 2.7–4.2V range and boost it up to a constant 5.0V, and that will let you run at 16MHz all the time.
If you decide to use 2 cells in series, that gets you a combined battery terminal voltage range of 5.4V to 8.4V. Because that’s too much to supply the ‘328P directly, you would put that into the Uno’s ‘Vin’ terminal, where its onboard ‘linear’ 5V voltage regulator will then supply the ‘328P with a nice constant 5.0V.
If you’re not drawing much power for Other Things connected to your Uno, then the Uno’s on-board 5V ‘linear’ regulator will happily cope with that without getting too hot. If you ARE powering “significant” other peripherals (a string of LEDs, a hungry GPS module, etc), then that could be a problem for heat dissipation in the Uno’s on-board 5V regulator sooner.
ETHER WAY, you’re still wasting a LOT of battery power (i.e. run time) - all that power (P = V x I) between 5.0V to whatever the battery’s terminal voltage is (between full & flat) has to be wasted as heat with a ‘linear’ voltage regulator. So in a 2-cell-in-series arrangement, I’d use a ‘buck’ switch-mode regulator to regulate that 5.4–8.4V from the battery back to 5.0V with typically 90+% efficiency and not much heat.