Selecting batteries for mobile robots application is a very important decision in the initial stages of designing a robot. The type and size of battery you choose for your mobile robot determines not only how long it will run between charges, but also how fast it will drive the motors, and how much current can be discharged at once. It is also important for a robot designer or hobbyist to understand the brand of batteries that are suitable for different robot applications.
Battery Specification vs Design Parameters of Mobile Robots
Batteries are rated by their output Voltage and Amp-hour (Ah) rating, which tells us how long the battery will supply power given a particular load. For example, a typical battery rated at 12V / 7.2Ah and after fully charged should supply 7.2A to a load for 1 hour at an operating voltage of 12V. If the supply current is reduced by half, the duration of supply will inversely double at the same operating voltage, all things being equal.
You might recall that arranging batteries with both series and parallel connections can provide multiple output voltages and higher Amp-hour (Ah) ratings. We often use these techniques to achieve a specific voltage with several smaller battery cells. Similarly, you can play around a combination of batteries of the same type to obtain either higher voltage or current to match the design parameters of your particular mobile robot application.
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Rechargeable Batteries vs SLI Batteries for Mobile Robots
Besides, rechargeable batteries are often recommended for mobile robots because they are more efficient for robotics projects. Most rechargeable batteries can supply voltage levels that are around 10% – 15% higher than their rated voltage when fully charged. This provides an added benefit for the mobile robot when operating in a rough terrain. Do not attempt to use a starting-lighting-and-ignition (SLI) type battery because it only provides a quick-start and the supply voltage is usually below the rated voltage.
Deep-Cycle Batteries vs Shallow-Cycle Batteries for Mobile Robots
Amongst the rechargeable batteries, use deep-cycle type of battery because they provide sustained energy, making them ideal for mobile robot applications that require more than a quick-start.
Type of Battery Chemistry vs Energy-to-Weight Ratio
Having established the specifications of your battery and made your choice for a rechargeable deep-cycle battery, the next task is the type of battery chemistry or technology (whether lead-acid Pb, Lithium-ion Li-ion, Lithium Iron Phosphate LiFePO4, Nickel Cadmium Ni-Cd, etc). Since the battery is practically integral to the mobile robot, a battery with higher energy-to-weight ratio should be selected. This will help reduce the overall weight of the mobile robot and increase efficiency.