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| 13 | replace various DC batteries (Figure 1). NASA reports the astronauts as "swapping five (5) aging nickel-hydrogen (NiH 2 ) batteries with two (2) new lithium-ion (Li-Ion) batteries and later moving on to swap one (1) more NiH 2 battery for a Li-Ion battery on the Starboard-6 truss structure worksite." Rechargeable batteries allow us to be unplugged even into the vast domains of space. Recharge Besides allowing us to go unplugged, secondary batteries are rechargeable. Rechargeable batteries can be recharged repeatedly (Figure 2). Recently, I returned home from one week's vacation. I immediately noticed my overgrown lawn because of the heavy rains in my absence. Coming home from work the day after my return, I knew the first thing I had to do was mow. An hour later, I was done, hot and sweaty from the 37˚C temperature ever common to Texas in the summer and full of ant or mite bites up and down my legs. By late evening, these bites drove me insane with the itching and the desire to scratch them, which we all know we are not to do. My only hope was to alleviate the pain was to go to bed and sleep it off. I took two antihistamine diphenhydramine (Benadryl) pills and went to sleep. I slept through the night and woke up refreshed and no longer itching. It turns out, all I needed was a recharge. As humans, we recognize that when we drain ourselves physically, mentally, and emotionally, periodically, we need to take time to recoup our power and energy. Humans biologically accomplish this through sleeping, a sort of biological recharging. Rechargeable batteries emulate this human capability to get reenergized. One important ramification of this is that battery costs must be reevaluated over time. In many cases, primary batteries are less costly to purchase. However, when the amount of current consumption is calculated over time, the need only to buy a secondary cell initially and then get many low-cost recharges out of it will make the economic benefits of rechargeable batteries stand out as very advantageous. The principle of the total cost of ownership (ToC) should be examined based on the context of the specific application. Another excellent side benefit of being rechargeable is the impact that this has on environmental issues. We desire to live in a world whereby humankind stewards its resources well and works to mitigate harm to the environment. There is general agreement globally that every business endeavor should commit to and work to achieve initiatives that promote greater environmental responsibility. Although the ecological impact is not often priced into a ToC calculation, it should be (Figure 3). Figure 2 Rechargeable batteries can get used more than once. (Source: Shutterstock) Figure 3 Rechargeable batteries help reduce waste. (Source: Shutterstock)