Battery building comes with its own dictionary of obscure terms that you might have never heard before. Below is a list of battery glossary terms to help you better navigate the world of DIY battery building and entertain your friends at your next dinner party.
Volts (voltage) – The is one of first measurements you’ll hear about a battery. Technically, voltage is a measurement of electromotive force between two locations, but we don’t really need to get into the physics of it. Basically, higher voltage means that electricity really wants to flow more, while lower voltage has less force trying to push those electrons along.
Amps (current) – Current is the rate of electrical flow. Basically, many more electrons moving down a wire means more current, and thus higher amps (the unit of current).
Watts (power) – Watts are a measure of power and are equal to volts multiplied by amps. So you can get high power with either high voltage or high current, or both. But low voltage and low current will always be low power.
Amp hours (capacity) – Amp hours are a measure of capacity. They are analogous to gallons or liters in a fuel tank. If you know the amp hours of a battery, and you know the current draw on the battery, you can calculate how long the battery will last. For example, a 10AH battery on an electric bicycle being powered by a 20A controller that is constantly pulling 20A will give you a run time of 30 minutes (10AH/20A = 0.5 hours).
C-rate – This is a very important specification for batteries and one that many people don’t understand. The C rate is the amount of current that a battery can handle and is ALWAYS based on the capacity (amp hours) of the battery. To determine the maximum discharge current of a battery with a c-rating of 3 and a capacity of 10AH, you simply multiply the c-rate by the capacity, giving 3 x 10 = 30A. That battery can safely provide 30A. If the c-rating of the battery was only 2, the battery would be capable of 20A. C-rates aren’t only used to represent maximum current draw though. They are often used as a demonstration of charge current. So let’s consider a 2AH cell. If that cell was tested at 1C, that means it was tested at 2A. If it was tested at 0.2C, it was tested at 0.4A. Got it?
Now imagine that we are building a battery with 5 of those 2AH cells in parallel. That would give us a 10AH battery. If the maximum discharge rate of those cells was 2C, the maximum current we could safely pull from that battery would be 20A. But what if we wanted to build a battery that could give us 30A? We could use those same cells, but we’d need more of them. We could build a battery with 8 of those cells in parallel, giving us 16AH. Now a 2C discharge would be 32A. Understand? If it’s still a bit complicated, try heading on over to the forums and we’ll help you further.
Charge and discharge rate – This is often related to the c-rate, and it’s just a measure of how much current is flowing. A battery cell might be rated for 10A discharge rate and 1.5A charge rate. A battery pack made of 4 of those cells in parallel would then be capable of a 40A discharge rate and a 6A charge rate. As a rule of thumb, you never want to exceed the maximum charge and discharge ratings of your batteries or cells, and it’s best to run your battery a bit shy of those maximum ratings when you can. Adding more cells in parallel or choosing a battery with a larger capacity (AH) will help you stay at a lower charge and discharge rate when measured by C-rate. Remember, a 5A charge on a 10AH battery is a higher C-rate than a 5A charge on a 20AH battery, even though it’s the exact same absolute current.
Terminals (cathode and anode) – The terminals are simply the contacts at the end of a battery or cell, with cathode meaning the negative terminal and anode meaning positive. They are simply the metal pieces that conduct electricity to the rest of your circuit. On a AA battery they are usually flat at the negative end and raised like a button on the positive end. On a car battery they are usually both posts that have wires clamped onto them. On an 18650 the negative terminal (cathode) is always flat and positive terminal (anode) is usually slightly raised, though not as high as like a AA or AAA battery.
Wire gauge – wire is measured in a number of sizes and units based on thickness. A quite common unit is wire gauge, usually AWG or American Wire Gauge. It’s a bit counterintuitive, but a smaller AWG size is a bigger wire, and vice versa. 12AWG is usually a thick discharge wire, while thinner charger wires might be 16 AWG or even 20AWG. Wires are often also measured in cross section size, were 12AWG is about 3.3mm2 while 16AWG is about 1.3mm2.
Conductor – A conductor is usually a piece of metal that can carry, or conduct, electricity. This can be a wire, a piece of nickel strip, or even tap water. Fun fact: pure, de-ionized water doesn’t actually conduct electricity. Most water outside of a laboratory is full of ions though including traces of salt. That’s what conducts the electricity.
Nickel strip – This is a band of nearly pure nickel metal that is used as a conductor. It usually comes in rolls or pre-cut strips and is either spot welded or soldered onto its connection points. Some nickel strip is actually nickel-coated-steel and not pure nickel. This is cheaper but has higher resistance. Always use pure nickel strip for any high power application.