Batteries for Arduino and Robotics projects

Because of the various options available for battery types, coupled with the variety of sizes, I often get asked how to choose a battery for a robot. This applies to more than just robots though, this article will explain important aspects to be aware of when choosing a battery for any electronics project. This is a comprehensive article on the various battery types and key features of each type.

If you want to skip all this I’ll tell you right now, my go to battery is a lithium polymer but if you’re not comfortable using and recharging lithium batteries then I’d recommend NiMH which are essentially rechargeable AAA, AA, C, or D batteries like Energizer Recharge.

Battery Features

It’s important to know the different properties of batteries so you know how to determine which properties are important for your project. The following properties of batteries are important to understand

Capacity

This is the current a battery can provide and is measured in Amp Hours (Ah) but more typically in milliamp hours (mAh). If a battery is 1000mAh it means it can provide 1A or 1000mA of power for about one hour. Likewise, it can provide 500mA for about two hours. Basically, if you divide your battery capacity by your circuit’s current draw you get the number of hours your battery will last… approximately.

Example power calculations

Circuit Draw (mAh)	Battery Capacity (mAh)	Power for (h)
500	1000	2
100	1000	10
2000	1000	0.5

Voltage (Nominal/Actual)

Nominal voltage refers to the voltage of a battery when it is discharged. For example, the following table shows nominal vs actual voltages of various battery types. Knowing the voltage of each battery is important so you know how many cells you need for your project. Each cell will increase the voltage by a multiple of the nominal voltage.

Battery Type	Nominal	Charged	Depleted (roughly)
Alkaline (AAA, AA, C, D)	1.5	1.5	1.0
NiMH (AAA, AA, C, D)	1.2	1.2	1.0
Lithium Ion	3.7	4.2	3.2
Lithium Polymer	3.7	4.2	3.2

Shape

Battery shape is important because your robot needs to be able to carry the battery around. With alkaline and NiMH batteries, you’ll have standard shapes like AAA, AA, C, D, and 9V. Lithium Ion has shapes as well, the most common being 18650 and Lithium Polymer (LiPo) batteries have no standard size. I like LiPo batteries because I can pick a size that fits my style project.

Connector

The connector is important as you need to be able to connect your battery to your circuit. Alkaline, NiMH, and Lithium Ion batteries all come in standard shapes as we discussed, these types of batteries will have “packs” available. Typically these packs will come in various sizes to allow for multiple cells. I’ll talk more specifically about LiPo connectors in the LiPo section as there are many options.

C Rating

A battery’s C rating will tell you what amount of power the battery can safely maintain. The C rating is a multiple of the battery’s capacity, so if a battery has a 2C rating it means it can supply twice its capacity in current output. Alkaline and NiMH batteries are going to have the worst C ratings, check out this article for an in depth look but as a quick overview Alkaline and NiMH were only able to provide about 1A of max continuous output. Most Lithium (LiPo or LIon) will provide around 20C or higher, this means if you have a 1000mAh battery, you can provide 20,000mA continuously. Keep in mind, this means you’ll only get five minutes of use from that battery. The high C rating is more helpful with larger batteries such as 2.2Ah or higher. High C ratings are required for projects that will use a lot of current draw like pushing full power on a drone or a large robot that can carry hundreds of pounds and has motors consuming upwards of 10A of current at any given time. Lead Acid batteries also typically have very large C ratings, this is why they are used for starting engines, large engines require a large surge of current to turn them over so many lead acid car batteries offer 80C or higher.

Rechargeable options

Not only whether or not your battery is capable of being recharged but what are the options of recharging. With most NiMH and Lithium options you get a charger with a fixed rate which is usually pretty slow (350mAh to 500mAh) because they don’t know what size battery you’re going to stick in there so it needs to be low to stay on the safe side. For LiPo (and LIon) batteries you can purchase one of a number of chargers that allow you to set the charging rate. If you want a set it and forget it and don’t want to mess around with this you can still purchase fixed rate chargers for your LiPo but they’re probably going to take a few hours to charge your battery.

Another aspect of battery recharge ability is how many times it can be recharged and if it has what is called “memory” and voltage depression concerns. Memory refers to a battery losing capacity over time, the first time it is charged it has 1000mAh, after 100 times it has 800mAh. Voltage depression is nearly the same but with respect to voltage and is due more to overcharging rather than the number of recharges. With voltage depression, a battery will not hold it’s nominal voltage as long as it used to however, it will still supply the same capacity of power which makes it different than “memory”.

Battery Types

If you don’t want to read all this riveting information on battery types, you can skip to my most commonly recommended battery types; Lithium Ion and Lithium Polymer or LiPo.

Lead Acid

I wouldn’t recommend a lead acid battery for a project unless you’re working on something that needs a whole lot of current (30A or more) like a very large robot. For that reason I won’t go into detail on these types too much. Even in cases where you need a lot of current I would probably recommend a different type of battery because lead acid batteries are typically heavy, bulky, and charging can take a long time compared to alternatives.

Some good applications for lead acid batteries might be

• Storing solar energy
• Large robots requiring a lot of current capacity at a low cost

Alkaline

Alkaline are the easiest to use as most people are very familiar with them, the most common sizes are all 1.5V AAA, AA, C, D, and then there is the 9V as well. I usually don’t recommend alkaline specifically because they aren’t reusable, they are good to have as backups if you are using rechargeable versions of these battery sizes.

Your projects are typically going to require 6V-12V which means, with the 1.5V sizes you’ll require between four and eight of them. With the different 1.5V sizes you get more current capacity or, in other words, they will provide power for a longer period of time. Usually the cheaper brands will offer less current capacity which is why the more well known brands cost more, they last longer.

Capacity

For Energizer Max batteries, you get the following capacities

Size	Energizer
AAA	1200mAh
AA	3000mAh
C	8000mAh
D	17000mAh
9V*	600mAh

*9V batteries are the worst, I almost never recommend these for projects

Voltage

Alkaline batteries are mostly going to come in 1.5V and 9V but do come in other more uncommon voltage ratings.

Shape

These are going to typically be your AAA, AA, C, D, and 9V shapes but as with the voltages, there are other more uncommon shapes.

Connector

You can find many different connectors for alkaline batteries, they come in singles, two packs, four packs, eight packs and even come in enclosed varieties. Most often they come with two bare ended wires for positive and negative which will plug right into your breadboard. They also have an option with a connector that fits most Arduino boards.

C Rating

Alkaline batteries have a low C rating compared to alternatives, these are fine if you don’t need more than 1A of continuous current.

Recharge Ability

Rechargeable alkaline batteries are hard to come by as they have mostly been replaced by NiMH. Alkaline has a low cycle count, it can’t be recharged very many times and a significant capacity is lost after each charging cycle.

Nickel Metal Hydride (NiMH)

These batteries are usually referred to as “rechargeable batteries”. These batteries come in the exact sizes as alkaline only these are rechargeable. One thing to be aware of here is that these have a nominal voltage of 1.2V rather than the 1.5V that alkaline provide. Measuring with a multimeter you may notice a voltage of 1.5 but they will almost immediately drop to around 1.2-1.3 for most of their use. So, if you have eight alkaline, your voltage will be 8*1.5 or 12V exactly but with NiMH you’ll get 8*1.2 or 9.6V so you’ll need ten rechargeable batteries to get the same output voltage as eight alkaline. It’s not that big of a deal though, technically an alkaline battery only runs at 1.5V for the initial few minutes, afterward it hovers around 1.3V which is roughly the same as a NiMH battery.

Ultimately, I’m not a huge fan of these either as they are bulky and the packs available don’t come in very many alternate sizes. They’re also fairly heavy in comparison to lithium alternatives.

Some good applications for NiMH batteries are

• If you don’t have access to or aren’t comfortable using lithium batteries
• Projects requiring ~5V since this only requires four batteries (remember, NiMH have an actual voltage of 1.2V, not 1.5V like their non-rechargeable alkaline counterparts)

Capacity

For Energizer Recharge batteries, you get the following capacities Note that C, D, and 9V capacities are greatly reduced from Alkaline

Size	Energizer
AAA	700mAh
AA	2300mAh
C	2500mAh
D	2500mAh
9V*	175mAh

*9V batteries are the worst, I almost never recommend these for projects

Voltage

NiMH batteries are mostly going to come in 1.2V and 8.4V, note that these are typically advertised as 1.5V and 9V but are not their actual voltages. They do come in other more uncommon voltage ratings but are more rare.

Shape

These are going to typically be your AAA, AA, C, D, and 9V shapes but as with the voltages, there are other more uncommon shapes.

Connector

Connectors are going to be the same as with Alkaline since these share the same form factor.

C Rating

NiMH batteries while not as low as alkaline, do still have a low C rating compared to alternatives, typically around 2C. NiMH batteries are fine if you don’t need more than 2A of continuous current.

Recharge Ability

NiMH batteries can be recharged anywhere from 500 to 1000 times. Careful with overcharging as this results in voltage depression which can make it seem as though your batteries don’t last as long. Voltage depression in NiMH can be more or less fixed by completely discharging and recharging the batteries few times.

Lithium Ion (LIon)

I think of Lithium Ion as the hybrid between LiPo and NiMH simply because, LIon batteries typically come in hard, rigid packages. They are the most expensive of all the types of batteries I’ll cover.

Capacity

Lithium Ion batteries have the best capacity to weight ratio of any battery which allows you to get long lasting power out of the same size package as NiMH or other batteries.

Size	Capacity
18650	~3000mAh
CR2032	235mAh

Notice the tiny CR2032 cell battery found in watches can provide nearly half the power of a 9V alkaline at a fraction of the size.

Voltage

Lithium batteries typically come in a 3.7V nominal voltage per cell, that’s 4.2 charged and roughly 3.2 discharged. There are other common lithium ion batteries such as “coin cell”, “button cell”, or “pill” batteries that you find in watches, hearing aids, remote controls etc, that have varying ranges of voltages but typically around 3V.

Shape

The most common shape, aside from button cell varieties would probably be the 18650 which has only grown in popularity since vape pens have grown in popularity as well. The 18650 lithium is also most commonly found in laptop battery packs and cordless tools. The lithium ion batteries found in your phone are actually Lithium Polymer.

Connector

These connectors are going to look very similar to the Alkaline and NiMH connectors, since LIons come in rigid body sizes. The most common is the 18650 battery holder which comes in various pack sizes. You can even find button cell holders. These packs will typically come with a mini JST connector or bare ended wire. If you don’t have the connector you can clip the connector off the end and plug the wires directly into a breadboard. Never cut black and red wires together, clip them separately or the tool will short the battery

C Rating

Lithium C ratings are largely dependent on their size, typical 18650 batteries will have between 2C and 10C but the rating aren’t generally easy to find.

Recharge Ability

Lithium batteries can be recharged up to 500 times. With regards to lithium batteries, these are the least fuss in that the chargers typically have a fixed rate and charge each cell individually since they are rigid bodies. It’s recommended that you don’t discharge lithium batteries too much as they can become unrecoverable (cannot be recharged) and could also damage the battery in other ways. I always keep my lithium batteries above 3.4V.

Note that Energizer lithium batteries are not rechargeable

Lithium (Ion) Polymer (aka LiPo)

Lithium Ion Polymer or LiPo, LiPoly, etc is nearly the same as Lithium Ion but comes in a soft form which makes these batteries the most susceptible to damage.

Capacity

I can’t create a table here since LiPos come in a nearly unlimited range of capacities. Common sizes include 2.2Ah (2200mAh), 5Ah, 1Ah but again, they can be any size which is why I prefer to use LiPos. For my robotic projects, building little line following robots, I typically use around 750mAh to 1000mAh and they last for a few hours of on and off testing.

Voltage

Like Lithium Ion, these come in cell voltages that are 3.7V each. However, LiPos come in battery packs as well, they are referred to as #S packs such as 1S, 2S, 3S, 4S, etc. The #S refers to the number of cells, with a 1S it is one cell so the voltage is 3.7V, with a 2S you have two cells so the voltage will be 7.4V.

# Cells	Nominal	Charged	Depleted (roughly)
1S	3.7V	4.2V	3.2V
2S	7.4V	8.4V	6.4V
3S	11.1V	12.6V	9.6V
5S	14.8V	16.8V	12.8V

Shape

LiPo batteries come in all shapes and sizes, you can get very flat, wide and tall batteries like you’d find in a cell phone, square shapes, rectangular shapes. This is another reason I like LiPos so much, because I can build a robot and then find a battery size that fits my needs to fill some empty space on the chassis.

Connectors

The most common types of connectors are shown below. Your battery will likely come with one of these connectors, I’ve included the name because you will need to find the other end of the connector so you can connect it to your circuit. The battery will not come with a way to connect it so you either need to find the connector and buy a couple or buy an adapter for a connector that you already have.

Connector	Notes
	Identified by its red color, this is common for smaller LiPo batteries
	Identified by its yellow color, the XT30 is smaller than the XT60 and the female end has more of a figure eight shape whereas the XT60 has more of a rectangular shape. This connector is common on smaller LiPo batteries
	Identified by its yellow color, the XT60 is bigger than the XT30 and the female end has more of a rectangular shape whereas the XT30 has more of a figure eight shape. This connector is common on larger LiPo batteries (2A or greater)
	Identified by its red color and T shape, the T connector or Dean’s Plug is common among smaller LiPo batteries.

C Rating

Typical C ratings are around 20C but I have seen over 100C but this is typically referring to burst current or very short durations of high current draw. I would try to stick with around 20C, 40C if you buy one the specifically states it can handle 40C such as the Turnigy Nano-Tech series.

Recharge Ability

Lithium Polymer batteries can be recharged up to 500 times. They are different from Lithium Ion in that they don’t always have a charger with a fixed charging rate. Sometimes you can get a charger that plugs into the balance port and plugs straight into the wall and you can simply forget about it until it’s done. Other chargers allow you to set the charging rate and you can choose from a direct charge or a balance charge. Direct charging is done by applying the total voltage (depending on the number of cells) to the battery output connector whereas balance charging is done by charging each cell individually. With a 1S battery these are both the same thing but for example, with a 2S battery, direct charging would supply 8.4V to the battery and balance charging would supply 4.2V to each cell. You can quickly determine the number of cells in a battery by counting the wires on a balance port. There is one ground wire and then a positive wire for each battery cell. So, a 2S battery will have 3 wires, a 3S will have 4 wires and so on.

Balance charging isn’t overly necessary unless you notice the cells are not around the same voltage or if you frequently discharge the battery quickly this can cause the cells to discharge at different levels. I generally direct charge my LiPos unless I notice the cell voltages differing by more than 0.2V.

You can check each cell’s voltage by using a LiPo battery monitor which plugs into the balance port, this can also sound an alarm when your battery reaches a certain level so I recommend getting one for each of your LiPos. They work for up to 8S batteries

Conclusion

I always recommend Lithium Polymer batteries due to their wide range of sizes available, their wide range of voltages available and because there is flexibility when charging them. If I want to charge them fast I can, but if I have the time and I want to ensure they last longer I can charge them slower. They are also very cost effective, I can pick up a two pack of 1000mAh batteries for around $20 and they will last for years. Just be sure to buy the connector you need in order to connect the battery to your circuit. And remember, never cut the black and red wires at the same time, the wire cutters will short the battery and it could explode.