Batteries

Batteries are everywhere these days as they can provide power on-the-go. This however is when things become confusing: There are…

• …primary batteries (that cannot be charged), and rechargeable batteries.
• …different chemistries (i.e. NiMH, Lead-Acid, LiIon, LiPo, LiFePo4, etc.)
• …different battery voltages and charging requirements

A great primer on battery fundamentals is this excellent video. It explains thoroughly how rechargeable batteries work, what the different cell chemistries are, and why some batteries are more dangerous than others.

Overview

A battery cell stores energy chemically, and can supply this energy as electrical current. That’s the common denominator of all battery cells. From here, it can get more complex:

• Chemistry:
  Depending on the chemistry used by the battery cell, it can be rechargeable, or it is designed for one-time use only (discardable).

  The chemistry also determines the maximum safe cell voltage (i.e. 1.2V for NiMH, 3.7V for LiFePo4, 4.2V for LiIon/LiPo). It also determines the shelf life and energy density.

• Battery Cell vs. Battery:
  Each battery cell has a fixed voltage that depends entirely on its chemistry. For example, all NiMH cells have a maximum voltage of 1.2V.

  In a battery, multiple cells are combined to achieve different voltages and/or capacities. By connecting cells in series, the voltage rises. By connecting them in parallel, the capacity rises. For clarity, batteries are often called battery pack, and even though battery cells have always the same voltage, battery packs can have all kinds of voltages and capacities.

• Safety:
  Some battery chemistries like lithium are so powerful that they need a BMS to protect them from damage and protect you from fire hazards.

  Typically, the BMS is built into the battery, and you should always make sure your battery has a BMS, but you can also explicitly get batteries with no BMS (unprotected). Such batteries have a balancer cable instead so you can shift the tasks of a BMS to external components and save weight and cost.

In this article you find answers to the following questions:

• What are the different chemistries used in batteries in general, and how do they differ in terms of energy density, shelf life, and cost?
• Why can discardable batteries not be recharged like rechargeable batteries?
• What are the chemistries used in rechargeable batteries, and how do they compare?
• What is the difference between a battery cell and a battery pack?
• How can I test the quality and state of charge of a battery?
• What is a BMS, and how can I find out if my battery has one?
• Why do some rechargeable batteries have no BMS and a balancer cable instead?
• What are fake batteries, and how can I identify them?

Hopefully this is helping you to pick the best battery type for your next project.

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