The Prius PHV Owners Manual says on pages 47 and 93 that the traction battery has a limited service life and its capacity, meaning ability to hold a charge, will reduce with time and use. It also says that this reduced capacity will decrease the EV driving range but vehicle performance will not significantly become worse. Owners can suppress this capacity reduction by following these five practices: 1. Avoid parking in sun on a hot day with the traction battery fully charged. 2. Avoid frequent and sudden EV acceleration or deceleration. 3. Avoid EV driving near the maximum EV speed of 62 MPH. 4. When not driving for a long time, discharge the traction battery to the level where only HV driving is possible. 5. Use the charging times, as much as possible, to fully charge the traction battery immediately before driving. To quote from Page 47: "The hybrid battery (traction battery) has a limited service life. "The hybrid battery (traction battery) capacity (the ability to hold a charge) reduces with time and use in the same way as other rechargeable batteries. The extent at which capacity reduces changes drastically depending on the environment (ambient temperature, etc.) and usage conditions, such as how the vehicle is driven and how the hybrid battery (traction battery) is charged. "This is a natural characteristic of lithium-ion batteries, and is not a malfunction. Also, even though the EV driving range decreases when the hybrid battery (traction battery) capacity reduces, vehicle performance does not significantly become worse. "In order to reduce the possibility of the capacity reducing, follow the directions listed on P. 93, 'Capacity reduction of the hybrid battery (traction battery)'."