Hey Rani,
Lead acid batteries are abundantly available. If you want to use something for demonstration, then get a small one like 6V 1.2Ah from
Katranji or a nearby electronics shop. They all operate in the same manner, what differs is the duration the battery operates without recharging which is noted in the current rating on the battery.
If you want, you can also buy a
6V lead acid battery charger kit from Katranji to demonstrate how the battery gets recharged.