How to check the state of health of a high voltage battery

Why does battery health need to be checked? 

All batteries lose health over time.  It is a normal characteristic of any battery whether it be for a mobile phone, or an electric vehicle (EV).  In an EV, a battery with lower health usually means a vehicle can travel less distance on a single charge.  It can also mean that charge times can be longer, as the charging speed reduces as the health of the battery drops. 

What exactly is battery health? 

In an electric or hybrid vehicle, battery health can be summarized in 3 areas.  The 1st is how much electricity the battery can hold compared to when it was new.  The 2nd is how fast the battery can accept a charge or discharge, and the 3rd is how long the battery is likely to last before it falls below a minimum expected performance. 

What is the minimum health the battery can be? 

Within the warranty period most vehicle manufactures state somewhere between 70%-80%.  This means that below this point, the battery is considered not useful for a vehicle.  However, this doesn’t always mean that the battery needs replacing.  If the vehicle had a 150 miles / 240km range when new, when the battery has 60% health, it would still have approximately 90m / 144km range – perfect for a city car.