Why Is It So Easy to Select the Wrong Battery for Your Application?

Anyone who has spec’d in a battery for a new application knows that what sounds on the surface like a simple and straightforward task can get very complicated very quickly. Need a battery to supply a motor with 10 watts for 1 hour? Simple, select a 10 Watt-hour (10Wh) battery, right? The only problem is that, depending on the battery chemistry, a 10Wh battery may only be able to deliver 10 watts to the motor for about 40 minutes before it uses up its available capacity.  

Using batteries for high power applications only makes the situation worse. Why? Every battery has internal resistance, which you can imagine as a tiny light bulb inside the battery. All of the current that is delivered to the motor has to go through the light bulb first. At very low currents, the light barely shines at all, and most of the power is delivered to the motor. But at the high currents that are required by high power applications, the light shines brightly, using up the power that would otherwise have been delivered to the motor.

This reduction in power comes in the form of a lower voltage across the battery terminals. So, if your high power application requires 48V, you may have to use a battery pack rated at 60V. And that is only the beginning: you still need to limit the battery’s depth of discharge to a level that won’t cause damage to the battery, and you may want to limit it further in order to extend the battery’s cycle life. And the list of caveats and gotchas goes on from there.

To make matters worse, these complicating factors are different for different battery chemistries, so selecting a Li-ion battery for an application requires you to follow a totally different set of rules than you would follow to select a lead-acid battery for an application. I know that an incomplete understanding of these issues has led to poor choices when pairing batteries to applications, and I also believe it has led to missed opportunities for developers of new battery technologies whose solutions don’t align with rules of thumb typically applied by those in the industry. Most of those rules of thumb are based on lead-acid batteries, and they simply don’t apply to other chemistries.

VtM has addressed this challenge by developing an economic optimization model that pairs batteries to applications while taking into account the most important of these subtleties and complexities. The model is extremely useful for both creating a short list of battery options for a given application, and for identifying the best applications to pursue for a new battery technology. To learn more, please send an email to jay@venturetomarket.com.