Powering an electronics project made up of more than one component each with their own power requirements can be an intimidating task. This is especially true when building robots with sensors, servos, motors, actuators and more! Unfortunately after having gone down many troubleshooting rabbit holes with my own projects, I’ve discovered that there’s no such thing as “the best battery” that works for every application. Each project is unique and selecting the right battery is about understanding which battery metrics are most critical to fulfilling your project goals. Here’s my step-by-step guide that explores the most popular rechargeable and “one use” options, their pros and cons and how to make the right trade offs that will make your electronics or robotics project a success!
Battery Metrics to Evaluate for your Project
Here are some of the most important battery characteristics you have to weigh in the process of choosing the best power option for your project. Rarely will you find the perfect solution so you’ll have to decide what trade-offs you’re willing to make.
This one is pretty easy and straightforward – how big is the battery? If you intend to give your project a professional look, then you’ll probably want to hide some or all of the wiring, components and battery. The larger the battery size, the more creative you have to get in order to elegantly conceal it. For example, if your project is a wearable, then choosing a lead-acid battery the size of a brick is probably not the way to go.
Battery Weight and Energy Density
A battery’s energy density is the amount of energy a battery holds compared to its weight and is measured in watt hours (wh) per kilogram (kg). Like battery size, energy density is an important factor in your project’s design. High energy density batteries can be useful when there isn’t much room for a battery but you need a lot of energy output.
The price of the battery or batteries you’ll need will impact your total project budget and final retail price point if it’s something you want to sell. In the early planning stages of your project, it’s important to start thinking of power requirements early on so you can not only make the proper design adjustments to accommodate the battery size(s) you’ll need but also fit within your overall project budget as well. As you may have guessed, the more power you want in a smaller, lighter package the more you’ll have to pay.
The voltage a battery provides is largely determined by its cell chemistry. For instance, all alkaline cells are 1.5V, all lead-acid are 2V and lithiums are 3V. Batteries are generally made up of multiple cells connected inside an outer case. So although a lead-acid cell provides 2V, you’ll usually see them sold as 6V, 12V or 24V options. Likewise, in smaller electronics or robots that have a 6V motor, you’ll commonly see 4 alkaline batteries connected in series in a battery holder to power it (1.5V x 4 = 6V).
Single Use or Rechargeable
Single use batteries are also known as primary batteries. These are less expensive, maintenance-free and have a long shelf life. They’re a great choice for low current applications and those that need intermittent use like toys, flashlights, smoke detectors or when charging isn’t possible like for pacemakers, watches or hearing aids.
Rechargeable batteries are referred to as secondary batteries and although they are more expensive than single use or primary batteries, they can be usually be recharged 100s of times and can be a more affordable option in the long run. They deliver more current and are best for projects that need continuous power like laptops, cell phones or smart watches.
Battery capacity is a measure of the charge stored in the battery. It’s usually measured in Amp-hours or mAmp-hours and represents the maximum amount of current that the battery can supply and for how long. Understanding battery capacity is important because that tells you how long a battery will run before it’s dead.
Typically, Amp-hours are used for larger batteries and mAmp-hours for smaller batteries used for powering consumer electronics. Most of the time you can find the capacity printed somewhere on the outer housing of the battery and other times you’ll have to look it up on the datasheet. For example, let’s say a AA alkaline battery has a capacity of 2500mA. This means that it could supply 2500mA (or 2.5 Amps) for one hour – or 1,250 mA for two hours, etc.
Theoretically you can calculate how long your battery will last with this formula: Battery lifetime (hours) = Battery capacity (mAmp-hours) / Current drawn (mA)
But what you’ll quickly find is that in reality you’ll generally get much less than what the formula tells you. There’s several factors that affect the rated battery capacity:
- Internal resistance: All batteries have some degree of internal resistance and as the cell(s) become exhausted, the resistance increases. At some point, the resistance gets so high that the external voltage will fall to a value where it can’t be used effectively.
- Discharge rate: If the battery is being discharged very quickly then the amount of current that can be extracted from it is reduced. This is because the reactants needed for the reaction don’t have enough time to get to their positions and only a fraction of the total reactants are converted to other forms. On the other hand, if the battery is being discharged at a slower rate, more energy can be extracted from it.
- Self discharge (age): This primarily affects rechargeable batteries but one-use batteries can also lose their charge over time.
- Temperature: At high temperatures, the battery capacity is typically higher than at lower temperatures. But operating at higher temperatures also decreases a battery’s lifespan. Rechargeable batteries are more sensitive to temperatures and run best at room temperature.
Types of Batteries For Electronics projects
Battery cell chemistry determines many of the properties that impact battery performance, making it a key consideration in battery selection. Here are some of the most popular types of batteries used in electronics and robotics projects along with pros and cons to help you make the right choice for your project.
These are the ultimate workhorses and the go-to battery for cheap power. Even though lead-acid batteries have low energy densities, no other battery provides as high a power rate as reliably and inexpensively and that’s why they’ve been in use for 140 years. But as the name suggests, the primary component of its chemistry is well, lead, so these batteries are heavy. That’s why you find them in applications like golf cars, forklifts, UPS (uninterruptable power supply) vehicles, back-up power, electric scooters and wheelchairs. Lead-acid batteries come in 2V cells so you’ll always see them in an even number of volts, the most common being 2V, 6V, 12V and 24V.
Pros: Cheap, powerful, easily rechargeable and high output power capability
Cons: Very heavy, can’t handle deep discharges well, and has a limited cycle count
If you’re working on a large robot project or any electronics project that needs lots of power, try using a lead-acid battery.
These are the most popular batteries you’ll find. Alkaline batteries are sold in just about every store so they’re great for projects that a user can service. They have low self-discharge which means a long shelf-life. Alkaline batteries have a higher power density than NiCads and a bit better than NiMh but are one-time use. They’re ideal for low current applications and are used in many consumer devices and products like TV remotes, wall clocks and toys. Cells are 1.5V and available as coin cells and sizes from AAAA to D cell. Having multiple sizes with a standard voltage allows you to size up when you need more capacity and capability.
The only exception are 9V batteries. They’re actually made up of 6 very small 1.5V batteries so they have very low capacity and capability for the price – they’re expensive for what you get. You’ll outgrow these after your first few electronics projects.
Pros: Easy to find and a long shelf life
Cons: Non-rechargeable and low power capability
If you’re working on a project and want to easily replace batteries, try using alkaline batteries.
NiCad (Nickel Cadmium)
These batteries have been gradually disappearing from the market since the 1990s. But I added them to the list because NiCad batteries are still used in devices like cordless phones, solar lights and RC cars where price matters more than performance. Battery cells are 1.2V and usually packed in groups of 3 to make 3.6V.
At the time, their ability to provide high discharge rates made portable electronics products practical when they first hit the market. But due to the toxicity of cadmium other batteries like Li-ion and NiMh became more favorable and have much higher power densities. NiCad batteries are great at holding a charge when not in use and can be charged and discharged more times than other rechargeable chemistries. But they do suffer from “memory effect”, a condition where if you don’t discharge the battery properly and then charge it to full capacity, you lose a bit of capacity every time because crystals grow on the battery plates.
Pros: Inexpensive, long lifespan and recharges easily
Cons: Lower power density, requires specific charging procedure to avoid memory effect and cadmium is toxic
If you want a low-cost rechargeable battery with a long lifespan, try NiCad batteries.
NiMh (Nickel Metal Hydride)
This is by far the most common battery used in mobile electronics projects and robots. NiMh batteries can be a good alternative to alkalines. They’re rechargeable and the combination of price, capacity and weight is hard to beat. Plus there’s almost no memory effect or specific recharging procedure so every charge should bring the battery up to full capacity. NiMh batteries have greater power density than NiCads but they can’t handle high discharge rates as well. Most do have a high self-discharge rate but there are a few low self-discharge batteries on the market.
The battery cell voltage is 1.25V which is less than the 1.5V of alkalines but more than the 1.2V of NiCads. Like alkalines, they come in standard sizes but with more power capability.
Pros: High power density, standard size and easy to recharge
Cons: Self-discharges quickly and service life isn’t as long
If you have a small to medium-sized mobile electronics project that draws more current, try NiMh batteries.
Li-Ion (Lithium-Ion) & LiPoly (Lithium Polymer)
These are among the most popular types of battery because of their light weight, high discharge rate and very high power density. Lithium Ion (Li-ion) and Lithium Polymer (LiPoly) voltages are available in increments of 3.6V, more than double the rest of the battery options. In addition to delivering a lot of power, they can also be recharged fast. Li-ion batteries are commonly found in smartphones, portable gadgets, and battery-operated consumer devices that are used for extended period of time. But you always have to use them in combination with a protection circuit that prevents them from shorting out and causing a fire or explosion.
Pros: Very light weight, high power, capability and cell voltage
Cons: Expensive and delicate
So What’s the best battery for your electronics project?
With so many battery choices it can seem overwhelming at first and choosing the right battery and configuration is crucial to getting the best performance out of your electronic, robot or animatronic project. But now that you understand battery characteristics along with the strengths and weaknesses of each battery type, you’ll be able to weigh the trade-offs and make the best choice to fulfill your project’s unique needs. It’s important to start thinking about power requirements early on in the design process – how many batteries you’ll need for all your components and where you’ll place them. Otherwise, you’ll most likely end up having to make drastic changes to your design after the fact.