A single 9-V alkaline battery can deliver a charge of 565 mA h. Two of these batteries are connected one after the other to power a 32 ohm heating resistor at 18 V, drawing 0.56 A. About how long will this heater run before the batteries are exhausted?

1. Two batteries connected one after the other are stated to deliver a combined charge of 565 mA h + 565 mA h = 1130 mA h, or 1.130 A h. 2. The heater draws a steady current of I = 0.56 A. 3. Runtime is the total available charge divided by the current drawn: t = charge / I. 4. Substitute with consistent units: t = 1.130 A h / 0.56 A. 5. t is approximately 2.0 hours. 6. 1.0 hour would result from using only one battery's charge instead of the combined charge of both. 7. 20 hours would result from a tenfold arithmetic slip in the current or charge value. _Source: OpenStax Physics (CC BY 4.0), Ch 19 "Electrical Circuits", section Boot Warmers_