Most cars (if not all) consume energy even when they are parked, with the engine off and no visible systems working. Electrical systems including the clock and on-board computer systems drain the battery little by little until they completely empty it.
When the energy level in a battery is low, it might prevent it from being capable to start your car and you will need a boost to get your car running again. In worse scenarios, batteries that are completely drained can get damaged and they need to be replaced.
Therefore, if you do not move your car for a long period (like during the lock-down period), then the extended lack of use might damage the battery and cause it to need replacement.
Check the operation manual of your car or contact your dealer prior to disconnecting the battery. (We are not sure if there is a car out there that would not like having its battery removed)
Disconnect the battery from you car to stop the energy draining.
To do so remove the cable from the negative port (has the minus sign "-" and is usually black colored).
Do not let the negative and positive cable exposed metal ends touch under any circumstances.