There is no doubt that batteries for your phone are different from those in your electric car. The application usually dictates the type and size needed. Today, we’ll explore the various batteries available and how to select the best battery size for your system.
Battery Cell Shapes
Battery cells come in four common shapes: button or coin, polymer or pouch, prismatic, and cylindrical. Each shape differs in size and chemistry to suit various applications.
Smaller cells are frequently connected in series or parallel to create larger batteries. For instance, deep-cycle lithium batteries are often composed of multiple cylindrical or prismatic cells.
Button Cells
Also known as coin cells, button cells are small, round batteries that resemble coins.
Housed in a metal case, they come in standard sizes based on diameter and thickness.
For instance, the CR2032 cell is 20mm wide and 3.2mm thick.
Typically non-rechargeable, button cells are common in small electronics that require minimal power. Their small size makes them ideal for portable or wearable devices like watches, car key fobs, hearing aids, laser pointers, and remote starters.
Polymer Cells
Pouch, or pouch cells, introduced 1995, lack a hard exterior casing and are sealed in a foil pouch. Their flexible electrolyte allows for thin profiles and custom shapes.
While offering high packaging efficiency and energy density, pouch cells are prone to swelling and penetration risks.
Standard Li-polymer cells are commonly used in handheld devices like mobile phones, tablets, and laptops. Curved polymer cells are suited for wearable devices, while large-format polymer cells are utilized in Energy Storage Systems (ESS) and electric vehicles.
Prismatic Cells
Prismatic cells are packed in durable aluminum or steel casings and come in limited standard sizes based on dimensions. Their low-profile design improves volume utilization in battery packs but can be expensive to produce.
Prismatic cells also have less efficient thermal management, a shorter cycle life than cylindrical cells, and may swell.
Today, Li-prismatic cells are used in devices like phones and laptops, as well as in larger formats for electric vehicles and hybrids.
Cylindrical Cells
Cylindrical cells, such as 18650 (18mm diameter, 65mm length), 26650 (26mm diameter, 65mm length), and 21700 (21mm diameter, 70mm length), are the most popular Li-ion rechargeable batteries.
Enclosed in a metal can, these cells are symmetrical and efficient, minimizing stress and pressure.
With higher energy density than flat cells, cylindrical cells are versatile and preferred for multi-cell configurations in various applications, including medical, military, consumer electronics, and electric vehicles. They are robust and offer higher energy density when used in battery packs, making them a top choice for many industries.
Battery Chemistry, Voltages and Amps
Battery Chemistries
There are four main chemistries for batteries: lead-acid, nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), and lithium-ion, each with various sub-chemistries.
The key difference among these chemistries is energy density. Lithium-ion batteries have the highest energy density, followed by Ni-MH, Ni-Cd, and lead-acid. Higher energy density allows for smaller, lighter batteries.
However, other factors matter when choosing a battery chemistry.
For example, lead-acid batteries excel as starting batteries due to their high cold cranking amps (CCA), making them better for starting applications than lithium-ion batteries.
Battery Voltage
Batteries vary not only in physical size but also in voltage. For instance, AA and AAA batteries usually have a voltage of 1.5 volts, while some deep-cycle batteries can reach up to 48 volts.
Here are the most popular battery nominal voltages:
- NiCd and NiMH: 1.20V/cell for consumer applications
- lead acid: 2V/cell
- LiFePO4: 3.2V/cell
- lithium-ion: 3.60V/cell
- deep cycle: 12V
- RVs, golf carts, and boats: 24V, 36V, 48V
A useful guideline to remember is that higher power requirements for an application necessitate a larger battery voltage. The power output of a battery is determined by multiplying its voltage and current measurements (volts x amps = watts). In high-power applications, using a higher voltage can reduce the current, which allows for the use of smaller cabling.
Battery Amps
The primary determinant of a battery’s size is its capacity, which is measured in amp-hours (Ah).
This capacity is calculated by multiplying the current (in amps) by the run time (in hours).
For example, a 100 Ah battery can supply approximately two amps for 50 hours or four amps for 25 hours. It is important to note that the capacity rating serves as an approximation and may not be exact.
Common Household Battery Sizes
AA and AAA batteries are commonly used in small household electronics due to their compact size and 1.5-volt nominal voltage.
AAA batteries, being smaller than AA batteries, usually have half the capacity. These batteries are often found in devices like remote controls and small flashlights that require minimal power.
On the other hand, C and D batteries are popular choices for larger household electronics. D batteries, larger than C batteries, provide approximately 50% more capacity and are commonly used in high-power applications such as portable stereos and industrial electronics needing longer operational times.
Lastly, 9-volt batteries, also known as E batteries, are rectangular in shape and commonly used to power devices like smoke detectors in households.
What Are Battery Group Sizes?
The Battery Council International (BCI) establishes standard group sizes for rechargeable batteries used in cars, boats, and RVs. These group sizes refer to the physical dimensions of the batteries but do not indicate their capacity.
Generally, larger batteries tend to have higher capacities; however, this is not always the case. There are more than 50 different battery group sizes available. The most popular ones are listed below:
| Group Size | L x W x H (mm) |
| Group 24 Battery | 260 x 173 x 225 |
| Group 27 Battery | 306 x 173 x 225 |
| Group 31 Battery | 330 x 173 x 240 |
| Group 34 Battery | 260 x 173 x 200 |
| Group 35 Battery | 230 x 175 x 225 |
| Group 51 Battery | 238 x 129 x 223 |
| Group 65 Battery | 306 x 192 x 192 |
| Group 78 Battery | 260 x 180 x 186 |
Some of our clients believe a larger group number signifies a bigger battery, but this is not true. As you can see above, a Group 31 battery is actually larger than a Group 51 battery.
Batteries for Cars, RVs, Boats, and Golf Carts
There is no universal battery group size that fits all cars, RVs, boats, or golf carts. Vehicle manufacturers provide recommendations to help select the appropriate battery size.
For passenger vehicles, common battery group sizes include 24, 27, 34, 35, 48, 49, 65, and 78. RVs and boats often utilize similar sizes.
Golf cart batteries are categorized with “GC”. The most common is the GC2 (6 volts), along with along with options like GC8 (8 volts) and GC12 (12 volts).
Choosing the Right Battery Size for Your System
Choosing the right battery size involves more than just selecting the largest one you can afford. Consider your the factors like power needs and available space.
Holo Battery experts can help determine the necessary battery size by providing your devices’ power consumption to calculate amp hours required. Contact our technical experts today, they are happy to help!
