Question: Alarge lithium-ion phosphate battery pack for an industrial application is expected to save $20,000 in annual energy expenses over its 6-year life. For a 3-year simple payback period, the permissible capital investment is $60,000. What is the internal rate of return on this $60,000 battery pack if it has a residual value of $10,000 at the end of 6 years? The MARR is 18% per year.