Complex sentence: At the same time, the leading manufacturer of pacemakers heavily invested in the development of nuclear batteries with similar projected life spans of 50-80 years, but they were quickly abandoned due to nuclear waste handling problems.
Split into simpler sentences: At the same time, the leading manufacturer of pacemakers heavily invested in the development of nuclear batteries with similar projected life spans of 50-80 years. These batteries were quickly abandoned due to nuclear waste handling problems.