The highest profile problems experienced by teams include the recent smoke and fume incident at Red Bull's UK factory, and the electric shock sustained by a BMW-Sauber mechanic at the Jerez test this week.
Toyota engine boss Luca Marmorini tells the German magazine Sport Bild: "All teams are having problems at the moment.
"Building a safe system is proving a difficult thing. For 2009, time is running out," he added.
"To me, it would be more logical to test it for a year before we use it at the races. For us at Toyota, safety has the highest priority," Marmorini said.
Williams driver Nico Rosberg explained: "For the first few races (of 2009), no team will be on the grid with KERS.
"It is Williams' plan to introduce it for the first race, but that is a big task," the German driver added.
Honda team principal Ross Brawn is believed to have said a similar thing.
Renault team boss Flavio Briatore told the German newspaper Bild-Zeitung: "If the system is not safe, we will not put it on the car."
Speaking for the drivers' safety union the GPDA, Mark Webber said: "Some teams are having problems with the chemicals that are used for the batteries.
"It is important to us that it is safe, when we are driving at 300kmh, or in the event of a heavy accident."