The new 120Ah lithium-ion unit replaces the 94Ah battery used by the existing i3, bringing an 9.2kWh increase in energy capacity for the quirky five-door hatchback at 42.2kWh.

In the standard 125kW i3, it provides a range of 310km, or up to 55km more than the predecessor model, on the newly introduced Worldwide Harmonised Light Vehicle Test Procedure (WLTP) emission regulations, according to BMW.

In the more performance orientated 135kW i3s, the new battery is claimed to bring a 40km improvement in range at an official 285km under the WLTP regulations.

BMW puts the power consumption at 13.1kWh and 14.6kWh respectively for the i3 and i3s.

Under every day driving conditions, BMW says the new 120Ah battery provides both i3 models with a realistic range of up to 260km, or 60km more than that quoted by the German car maker for the existing i3 with its 94Ah battery.

Under the previous New European Driving Cycle procedure the older i3 94Ah and i3s 94Ah posted ranges of 300km and 280km. When the new 120Ah versions are measured on the same test procedure, BMW says they offer a respective 359km and 345km.

BMW i is remaining tight-lipped on the weight of its latest battery. However, it claims  the 0-100km/h times for the rear-wheel drive i3 and i3s remain virtually unchanged at 7.3sec and 6.9sec respectively, with the 80-120km/h times put at 5.1sec and 4.3sec.

The new battery, developed in partnership with Samsung, retains the same dimensions as the unit it replaces, enabling it to be packaged in the same dedicated space within the floor of the i3 as the unit it replaces.

BMW puts the recharge time of the battery at 15 hours on regular 2.4kW mains electricity. This is reduced to 3.2 hours on an optional BMW i Wallbox, which provides three-phase charging at 11.0kW.

On a fast charging DC system operating at 50.0kW, the recharge time is a claimed 42 minutes.

Since its introduction in 2013, the i3 has been offered with three different batteries, including the original 60Ah unit and the 94Ah unit of previous models, with respective energy capacities of 22.6kWh and 33.0kWh.

In addition to the new battery, BMW has also announced a new optional sports package for the i3 as part of changes being brought to the 2019 model. It includes a sports suspension with a widened front track, 10mm reduction in ride height, uniquely tuned springs, dampers and anti-roll bars and 20-inch wheels.

Further changes include new exterior colours, revised upholstery combinations for the interior, optional adaptive LED headlamps and new iDrive infotainment functions, including a LAN hotspot capable of supporting up to 10 devices.

Sales on the new i3 and i3s are planned to get underway before the end of the year.