Engines and fuel economy
Most hybrids use small, four-cylinder gas engines that are more efficient than larger V6s and V8s. Hybrid SUVs, however, come with either four-cylinder, V6, or V8 engines, depending on the size. Some SUV or luxury-car hybrids also offer V6 or V8 engines. The V6-powered hybrids are smooth, quiet, and quick. And big, V8-powered hybrid SUVs and pickups are responsive and offer large towing capacities. Four-cylinder models run the gamut in terms of refinement, but most four-cylinder hybrids are quieter and feel less strained than equivalent gas-only four-cylinder models.
Most hybrids come with some sort of continuously variable transmission (CVT). Some hybrids use conventional belt-type CVTs. More use planetary gear sets with infinitely variable ratios in a virtually wear-free design.
Hybrid SUVs can be front, rear, or all-wheel drive. Most small-car hybrids are front-wheel drive, while luxury-car hybrids are rear-wheel drive. All-wheel-drive versions of the Toyota Highlander and Lexus RX 450h power the rear wheels via an extra electric motor on the rear axle of a front-wheel-drive design. It's light, simple, and efficient, and we've found it works well enough. Unlike traditional AWD vehicles that compromise fuel economy, hybrid AWD vehicles can often avoid such a penalty by using electricity to drive those extra wheels.
Conventional hybrid batteries of nickel-metal hydride are quickly being replaced by lithium-ion batteries, which are smaller and lighter, for better efficiency. Lithium-ion batteries also come in several varieties: Some variations are more stable and have less power. Others have more power, but require more robust external systems to guard against fire and prolong their life. So far, the question of which systems work best in cars has not played out.
Nickel-metal hydride hybrid batteries typically have very good reliability in our Annual Auto Survey of our subscribers. Lithium-ion batteries are too new to have a proven track record. Automakers are required to warranty the batteries on any hybrid as an emissions control part for eight years and 80,000 miles in most states. In about 10 states, they're required to warranty them for 10 years or 150,000 miles, so the automakers have a vested interest in making them durable. Outside the warranty period, nickel-metal hydride battery replacements can run as much as $3,000, but replacements have been relatively rare. And unlike in gas-powered cars, transmission replacements are almost unheard of.