B.T.ACT

Charge means to impose a burden, duty, obligation or lien to create a claim against property. A rent is a contract conferring a right on one person to possess the property belonging to another.So, rent is a charge through which the landlord claims right over his property . It is the first charge to prove tenancy.

1.A stated return or payment for the temporary possession or use of a house, land, or other property, made, usually at fixed intervals, by the tenant or user to the owner.

2.To get the temporary use of (a car, tool, furniture, etc.) by paying a fee.

Charge means  here I think to use the word of levy is the best one.

It is the right of the property holder to charge rent  on his or her property , which has been let out for rental purpose.

Tenancy creates rights to use the property in the agreed manner in consideration wth by paying some considered money that is you are saying charge/rent.

For the valid tenancy one must paying some charge. If some one enjoying property without giving charge/rent then he is not a tenant.

Thats why it is said rent is charge of tenancy. Which proves tenancy.