Nissan Leafs, which go about 107 miles on a charge, sometimes end up relegated to commuter cars due to battery-range worries. The mass-market, standard Tesla Model 3 can go double that but still can be disconcerting on long road trips. Both batteries could work up to 50 percent longer with a new device. It reconfigures modules — clusters of battery cells — in electric cars to be online or offline depending on whether they’re going to pull down the other modules.