It's my understanding that a person should never use a modified sinewave
inverter with a laptop, that we should always use pure sinewave
inverters with laptops, as the modified sinewave units are harmful to
the life of the laptop's battery.

Question #1: Is this true?

Question #2: How do I tell the difference? I have 2 inverters I use on
my boat, each from a different manufacturer, and neither one says
anything about the sinewave characteristics.