Often old dead lead acid batteries may be too damaged to start a vehicle, but may be revived and suitable enough for solar recharge to run small devices around the property. Such as security cameras, lights, sensors, mobile phones, small pumps, irrigation solenoids, wifi relays, smart IoT, Raspberry Pi’s, etc.
This may be a highly dangerous method and should not be attempted without full awareness of all the risks and safety gear and precautions to avoid injury and explosions.