Method for diagnosing the state of health of a battery

1. A method for diagnosing the state of health of a battery, comprising the following steps:

partially discharging the battery at a constant current,

measuring the battery voltage during partial discharging,

determining a first state-of-charge value from the battery voltage during partial discharging,

measuring the open circuit voltage of the battery and determining a second state-of-charge value from the open circuit voltage, and

calculating, with a processor, the state of health from the difference between the first and second state-of-charge values.

2. The method according to claim 1 , wherein the state of health SOH is calculated from the relationship

SOH

=

100

-

100

·

(

SOC

2

-

SOC

1

)

100

-

SOC

1

,

where SOC 1 is the first state-of-charge value and SOC 2 is the second state-of-charge value.

3. The method according to claim 1 , wherein the partial discharge current is comprised between C N /10 h and C N /1 h, C N being the nominal capacity of the battery.

4. The method according to claim 3 , wherein the partial discharge current is comprised between C N /5 h and C N /3 h.

5. The method according to claim 1 , wherein partial discharge takes place during a time period such that the decrease of the charge of the battery is comprised between 0.5% and 2%.

6. The method according to claim 1 , wherein partial discharge takes place during a time period comprised between 20 seconds and 10 minutes.

7. The method according to claim 6 , wherein the partial discharge time period is comprised between 1 minute and 3 minutes.

8. The method according to claim 1 , further comprising

disconnecting the battery during a time period comprised between 60 and 300 seconds, before

measuring the open circuit voltage of the battery.