[DannyTN]

Acme Pacemaker - Operating Instructions.

• Do not operate at extreme temperatures
• Do not engage in extreme sports.
• Do not climb Mount Everest or other high mountains.
• Do not take it out and play with it.
• Do not pass large electric currents through your chest.
• Do not ...

[Ingtar]

Most likely the do not that got them was, do not allow the battery to get too cold, a la electric cars.