Tech mogul Elon Musk has started discussing the possibility and potential of battery-powered electric airplanes and believes they could be viable in about five years.

This weekend, Musk updated his expected timeline for the energy density to improve enough to enable battery-powered airplanes, Electrek reported on Monday.

When a user questioned Musk, "Is it possible for planes to fly off of a battery? Or is there not a powerful enough battery yet?" the Tesla and SpaceX CEO replied, "Yes, but still a bit too limited on a range. That will change in coming years as battery energy density improves."

Musk explained that jet fuel beats batteries when it comes to energy density, but the efficiency gains mean that so much energy potential is not needed, the report said.

"Jet (kerosene) has much higher energy density than Lithium-ion (Li-ion), but electric motors weigh much less and convert stored energy to motion better than combustion engines," he wrote.

Musk estimated that Li-Ion batteries would need to achieve a 400 Wh/kg energy density in order for batteries to beat kerosene and his electric aircraft to be viable.

Today, battery cells with high cycles are achieving about 300 Wh/kg of energy density.

Musk has long been talking about all modes of transport going electric at some point - except for rockets.