The seller has to pay only for the electricity actually consumed by him up to the date of handing over possession of the flat to the buyer. In fact on the day he vacates the flat the seller and buyer should jointly take the meter reading and the seller should pay to the buyer the cost of electricity from last bill paid by him up to the meter reading. Any deposit with the electricity supply company is a security against default in future payment by the actual consumer. The default amount will be based on the actual consumption. It is only logical that any security deposit is the liability of the new consumer. In fact if the seller had already paid the deposit the buyer should reimburse the amount to him, unless the sale agreement clearly states that the payment made for the flat included the security deposit also.
Different electricity companies follow different procedures. I am residing in a flat in Mumbai where electric supply is from BEST. When my father was alive the flat and electric supply were in his name. When my father died the Society transferred the flat to me as his nominee. I applied for transfer of the electricity connection to my name along with the deposit. BEST wanted me to make a fresh deposit in my own name. They said that they will refund the old deposit to the heir of my father on production of necessary proof. Hence I paid a fresh deposit and collected back the old deposit after producing proof that I was the legal successor to my father.
Hence in the absence of any specific statement regarding the security deposit in the sale agreement the liability to make security deposit to cover liability for future consumption shall be on the buyer of the flat and electricity connection only. Actual consumption of energy has to be differentiated from liability for future consumption.
When my tenant at Chennai was asked to pay additional deposit for increase in energy consumption he only paid the amount. He got it reimbursed from me when he vacated the flat.
If you have any further question ask me here only and not by PM, so that other members can also see if they wish to.