Just a few months ago we asked readers to name the reason why they haven’t yet made the switch to a green car, with price proving to be the ultimate stumbling block. Now anyone hoping to jump on the plug-in hybrid electric vehicle bandwagon is likely to face a similar struggle.

A new report from the National Research Council has outlined that costs of plug-in hybrid electric vehicles are unlikely to drastically decrease in the near future, primarily due to their lithium-ion batteries.

The report looked at two configurations – 10mile all-electric range and 40mile all-electric range. The PHEV-10 has a larger battery pack than a regular hybrid electric vehicle and costs around $6,300 more than that of an equivalent sized mid-size car. Meanwhile, the PHEV-40, similar to the Chevrolet Volt, would cost about $18,100 more.

It is expected that costs will decline with technology improvements and economies of scale. However, lithium-ion batteries are already produced in great numbers for consumer devices and are well along the learning curves. The report suggests that the cost to manufacture these vehicles will decline by about one third by 2020 – but only slowly thereafter.

The report outlines that while it is possible breakthroughs in battery technology will greatly lower costs, at this point it is not clear what sorts of breakthroughs may become commercially viable. Furthermore, if they occur within a decade they are unlikely to have much impact until 2030.