The new battery that will be the lynchpin technology for the next generation of Formula E cars went through its first full race simulation test earlier this month.
The McLaren Applied Technologies-supplied battery, which will be introduced for the 2018/19 season will almost double the amount of usable energy to 54Kw/h so drivers can complete an entire race distance in one car.
It underwent a crucial simulation after months of single-cell and module-cell testing assessments, with on-track testing planned for October this year.
Professor Burkhard Goschel, president of the FIA's Electric and New Energies Championships Commission, told Autosport progress was being made with the battery but that the aggressive timeframe of the track testing is a challenge.
"It is proceeding well but we know that it is tight time wise and we will see this summer where we are at the end, but all signs which are coming out are looking positive," said Goschel.
"We made some first tests. There have been two samples at the end where they [the quality of the cells] stayed at the same energy content with 54kW/h and so it looks positive in this way but there are still a lot of things to do."
"[A full simulation] has been done and it shows up as being very positive and we can show that simulation is nearly the same reality.
"We still have some issues and with the timing, we just have to get ready with the main issues with the functional testing."
Goschel also confirmed that the biggest challenges were cooling and weight.
The new car is currently due to weigh 930kg, 42kg heavier than what was initially pursued.
"One issue always with the battery and the electrical drive is the cooling because the load in our case is a very, very strong one," he said.
"We will be recharging very deeply and the inner-resistance goes up and the requirement for cooling is going up.
"From the first season we have managed it, and I think we can manage it now too.
"The weight is getting tight. Because we have had some additional cells to meet some additional requirement which came up so we added some.
"We are under pressure with the weight, this is true."
Power will increase from 170kW to 200kW for the race and from 200kW to 250kW for qualifying in 2018/19.
Autosport understands that the new generation battery will have a significantly greater energy density as its composition is different to the current Williams Advanced Engineering unit.
The new battery is believed to contain 209 cells, an increase of 44 over the first generation of battery.
It is understood that McLaren Applied Technologies' Anthony Law will be the engineering lead for the Formula E project.