Benchmark testing of battery capacity needs to be introduced to help boost confidence in electric commercial vehicles when they reach the used market.

Ken Brown, valuation manager for CAP Red Book, which is used as a benchmark guide to used commercial vehicle trade values, said the testing is necessary due to the reduction in charge-holding capacity over a battery’s lifespan.

Because there is currently no way for second owners to know how much charge a battery will retain there is downward pressure on residual values.

“The problem is compounded by the fact that replacement batteries can cost several times what you paid for the van in the first place,” said Mr Brown.

He called for an independently-verified method of determining true battery capacity at disposal time.

“This would also enable us to set more accurate residual values which would help manufacturers, leasing companies and traders in the used markets alike,” he said.

“We are receiving an increasing number of requests for residual values from contract hire and leasing companies for battery powered electric vehicles.

"Clearly these ultra-clean vehicles have an important role to play as emissions increasingly dominate the taxation agenda and cities introduce measures to control CO2 and other emissions with bans and tolls.

“Establishing a benchmark is essential to creating confidence in this area of the market.

"Realistically, nobody would expect a five year old battery to have 100% of its original capacity.

"But if it can be established that the norm is, say, 85% then that could form the basis of CAP’s standard condition criteria for electrically powered vehicles.”