Patent ID: 8310198

Claim:
A method for charging a lithium ion secondary cell, which is used as a power source for driving and mounted in a hybrid electric vehicle, the method comprising the steps of: determining whether a value of a physical quantity corresponding to a storage amount of the lithium ion secondary cell has lowered to a first predetermined value; determining whether the hybrid electric vehicle is in a travel stop state; and when it is determined that the value of the physical quantity corresponding to the storage amount of the lithium ion secondary cell has lowered to the first predetermined value and in addition when it is determined that the hybrid electric vehicle is in the travel stop state, charging the lithium ion secondary cell until the value of the physical quantity corresponding to the storage amount of the lithium ion secondary cell reaches a second predetermined value while the hybrid electric vehicle stops running, wherein in the step of charging, a period during which the lithium ion secondary cell is charged is split into two or more split charging periods and non-charging periods provided between the split charging periods, and charging is performed in the split charging period and at least one of suspension of charging and discharging is performed in the non-charging period, and the length of each of the split charging periods is not less than 40 seconds.