ENG | Arduino: Battery power
Intro
What are suitable batteries for powering Arduino or microcontrollers in general?
Hopefully, Arduino (or rather ATmega328P controller) can be powered by basically anything between 1.8 and 5.5V, but
- Brown-out detection fuses have to be programmed accordingly (these shut down the microcontroller when voltage is below a certain threshold)
- Frequency should stay within the save operating limit (that’s why 3.3V Arduino Pro Mini has 8MHz oscillator)
- Logic inputs should not see higher voltage than VCC
- TODO: verify ADC conversion
- However, various sensors, memories, SD cards, … may have different requirements
Note about Arduino
Note that for low power applications, Arduino Uno, Nano and it’s clones have very cheap, inefficient linear voltage regulator such as AMS1117 which consumes about 5mA at 1.5V voltage drop and requires 1V drop so to power 5V Arduino, 6V and above is needed and higher the voltage means that more energy is wasted as heat. For projects which are not intended to run for a long time, it does not matter - use any rechargable batteries with over discharge protection. For projects running for days, buy either Arduino Pro Mini (preferably 3.3V model) or ATmega328P chip, oscilator crystall and few parts such as capacitors.
I did some research about battery types, here’s a summary of my findings.
Types of Non-rechargeable Batteries
This chapter is here just for reference. I do not recommend using these to power Arduino projects, but for example, CR2032 batteries are used as a backup for real-time clock and it’s good to know why not to power Arduino from them and what to consider.
Zinc (ZnS)
Ancient type, should be avoided.
- 👎 Very low capacity
- 👎 Leakage
Alkaline
Infamous for leaking, cheap primary batteries. They start close to 1.6V and discharge is quite linear to 0.8V, although battery drop above 1.4V and below 1.1V is steeper.
- 👍 -20C operating temperature
- 👌 Energy density on par or slightly above NiMH (about the same for volume, but lighter)
- 👎 Tendency to leak corrosive potassium hydroxide, especially when discharged. This reacts with CO2 in the air and forms potassium carbonate.
Lithium (Li/FeS2, Lithium iron disulfide)
Lithium/Iron Disulfide non rechargeable batteries. Different than Lithium-Ion or Li/MnO2 button cells.
Energizer L91 Ultimate Lithium (L92 for AAA), Varta (Ultra) Lithium 6106 (AA), 6103 (AAA), GP15LF (AA), GP24LF (AAA)
- 👍 15-25 years storage time
- 👍 15 grams for AA battery
- 👍 -40C to 60C operating temperature
- 👍 Suitable for high current (2.5A continuos)
- 👍 Highest capacity for AA/AAA batteries as far I know (3000-3500mAh, >4Wh)
- 👎 Very expensive
- 👎 A bit higher voltage with a very small load
I never used these. They can be suitable for a datalogger running during really harsh winter. They also have significantly higher capacity when they are discharged fast. Maybe they are good as a backup for an AA battery-powered headlamp in the winter (let’s admit that such a headlamp is not the best idea in the first place, due to low battery capacity)
Energizer and Varta have the very same specs (but older Energizer datasheet differs)
Lithium (Li/MnO2, Lithium manganese dioxide)
Typically as button/coin cells
These are suitable only for low-power applications and their capacity is severely reduced with increased load (or low temperature). Curiously they behave better in hot environment. I accidentally discovered they exist in AA size with 2000mAh/3V, but their max continuous current is still 15mA.
- 👍 7-10 year shelf live
- 👍 small size
- 👍 quite stable voltage during discharge at room temperature or above
- 👍 good energy density (power/size ratio)
- 👎 3mA max continuous discharge current (Varta CR2032)
- 👎 10mA max current pulse (Varta CR2032)
- 👎 230mAh capacity
- 👎 Expensive
- 👎 While they can operate in low temperatures, their voltage and capacity are reduced.
By the way, CR2032 has dimensions 20x3.2mm
Types of Rechargeable Batteries
NiMH (Nickel-Metal-Hydrid, MnO/Zn)
The Nominal voltage is 1.2V, but they have roughly 1.45V fully charged, then the voltage drops slightly below 1.3V and once it drops below 1.25V they are almost empty. The advantage is that they are time-proven, safe, and safe to overcharge (unless the current is too high) and they just get warm when they are fully charged. The disadvantage is that once they are deeply discharged, they are detected as defective by most chargers (ones that are not completely dumb but do not have battery regeneration on the other hand)
- 👍 Widespread
- 👍 Safe
- 👍 No leakage
- 👍 Chargers usually charge cells individually as they are not in battery packs.
- 👌 Charge rate could be 1/16C up to 1C (curiously, often the only way how to change charging current is to insert more batteries, 1C is current as a fraction of capacity, e.g 2A for 2000mAh battery)
- 👎 Low energy density per kilogram (heavy)
- 👎 Voltage is not the best for powering some devices directly.
- 👎 Hard to bring back to life when deeply discharged (e.g. used in toys)
- 👎 When connected in series, weaker battery may discharge faster and be damaged by a deep discharge.
Interesting videos:
- GreatScott! -=- Are AA NiMH Batteries obsolete?
- bigclivedotcom -=- Charging NiMH cells - smart vs dumb chargers
Li-Ion
They have the highest energy density (as of 2024) The nominal voltage is 3.6-3.8V, the maximum is 4.2 or 4.35 depending on the exact chemistry, the minimum is 3V. Their disadvantage is that they may catch fire which cannot be extinguished by water because as they burn, more oxygen is released than consumed by fire. The risk of fire is due to overcharge, short circuit, and mechanical damage. In many countries, they can’t be sold without a built-in protection circuit.
- 👍 Widespread
- 👍 High energy density (headlamps, drones, phones, …)
- 👍 Often optimized for fast charge or high currents
- 👍 BMS modules and chargers for battery packs are easy to find
- 👎 Voltage is not the best for powering MCUs directly (but could be fine)
- 👎 Should have built-in protection (or be rated for professional use only)
- 👎 Overcharging is dangerous
- 👎 500-1000 charging cycles
- 👎 Capacity loss with age
- 💥 Infamous for fire hazard, burn violently
Curiously Li-Ion batteries have huge disadvantage: they offer least charging cycles and they are used in applications when they are charged most often (phones, notebooks, wireless headphones) - and they are not easily replaceable.
Li-Ion button/coin cells
By the way, Li-Ion coin cells exist: LIR-2032
- 👎 Low capacity (35-40mAh for LIR-2032)
- 👍 Much higher discharge current than CR-2032 (70mA)
Li-Po
Same as Li-Ion except a package is a plasic pouch.
LiFePO4 (LFP, Lithium-Iron-Phosphate)
These are technically Li-Ion batteries with some pros and cons. First, they burn too if they are severely damaged. But they burn slowly and they should not ignite when overcharged, shorted, discharged, and so on - but they may inflate, leak or release some steam. A protection circuit is mandatory regardless. They also have different voltages with very flat discharge characteristics similar to NiMH: Fully charged battery cell has 3.65V, but as they are discharged, voltage rapidly drops to 3.3V and stays somewhere between 3.25 and 3.1V. Once voltage drops to 3.1V it almost does not matter if the circuit is cut off at 3V, 2.8V or 2.5V, because at 3.1V they have like 15% capacity remaining, at 3V it might be last 5%, and at 2.5V there is a risk of permanent damage due to self-discharge and they should not be stored in a discharged state (the same is true for Li-Ion)
- 👍 Voltage suitable for powering 3.3V electronics
- 👍 Cheap (especially without protection circuit)
- 👍 There are High-C types for fast charging and high currents, with reduced capacity and charging cycles
- 👍 2000+ charging cycles
- 👍 Slower aging
- 👌 Do not (easily) burn, could release gasses, smoke, or inflate
- 👌 Moderate energy density
- 👌 Very flat discharge curve - hard to guesstimate remaining capacity, on the other hand, it’s a stable 3.2V source
- 👌 Charging from 0.1C to 1C
- 👎 Destroyed when deeply discharged
- 👎 No widespread, need a special charger
- 👎 Should have built-in protection (or be rated for professional use only), but protection circuits with over current protection suitable for one battery seems impossible to find (except ebay: 1, 2)
It may seem like LiFePO4 has the most disadvantages, but it depends on their weights. The difference between opens portal to hell at first opportunity vs smokes and burns like a wood when you hammer a nail into it is a considerable difference and there are many YouTube videos on that topic.
My issue is that they seem to be sold always without protection (18650 type), my Voltcraft IPC-4 which is rebranded DLYFULL Smart A4 charger needs to select battery type by holding MODE button within few seconds after battery is inserted and can possibly overcharge it otherwise (and it seems to be an issue with many other versatile chargers).
Otherwise, it seems that LiFePO4 is used for applications where fire hazard is important while energy density is not: camping, solar power storage, boats, …
They also have significantly better life time compared to Li-Ion.
Basically as a replacement for lead-acid batteries.
For powering MCUs, they seem ideal, but it’s important to keep in mind that discharging them below a certain threshold (2.5V) can damage them and short circuit as well.
It’s not clear what happens when LiFePO4 is charged over 3.65V. According to some sources it gets a bit damaged, according to others, the voltage starts rising rapidly beyond a certain threshold and once charging stops, it returns to its safe zone shortly and there’s no reason to panic if charging stops at 3.8V. So monetary overcharging is likely harmless, while applying 5V to the battery for a few minutes is not.
Further exploration
- Can we power Arduino for powerbank in such a way it does not shut down due to low current draw?
- Can we automatically disconnect Arduino when input voltage drops to prevent damage of LiIon/LiPo/LiFePO4 or NiMH batteries?
- Can we build over current protection and reverse polarity protection and combine them? -> let’s explore logic level MOSFETs.
Summary
I would personally stick with NiMH or experiment with LiFePO4.
Li-Ion batteries have no advantage other than being able to provide high current and being lightweight, which is crucial for some applications, but not for powering electronics which is not portable.
LiFePO4 have the advantage of powering 3.3V devices directly and being cheaper than three or four NiMH batteries.
But price of 18650 LiFePO4 can vary wildly: they are either cheap (2.5-6EUR) or they are expensive (15EUR+) with built-in protection circuit and welded contacts.