How to dispose old expired laptop battery?

You have few options to approach in this case.

1. Dell's asset care and recycling unit.

Dell takes care of the unused batteries and the laptop. You can contact their asset care division. You may not get paid for this but you'd get some points or voucher at the most or nothing.
You can read more about the process here : http://www.dell.com/learn/in/en/incorp1/campaigns/global-consumer-service-contracts?s=corp

2. Karmacycling

This site seems to be accepting most of the electronic parts for the recycling. Check if you can sell the battery to them. It seems like currently they take product as a whole. So you may have to get in touch with them for the sales. Check out their website for more information : http://www.karmarecycling.in/index.php

There are few other websites that you can approach. Not sure if those sites are going to be good depending on local limitations.

There are some companies in India which are collecting the e-waste and they have even collection centres for it.

One such company is www.ecoreco.com and if one is interested in disposing his laptop battery then one can communicate to them at ewaste@ecoreco.com or phone to them at 1800 102 1020.

Another online entity is call2recycle who is a NGO and also help in getting the old laptop batteries. You can visit their website for more information.

Another option is to contact the supplier which in your case is Dell. They will also direct you for giving it to their collection center or even ship it to them.

Now a days due to more awareness for environment upkeep there are many agencies involved in such greener acts and the concerned citizens can take this as advantageous for their disposal of hazardous items.

You can sell out those old unused laptop batteries to the scrap vendor or the respective support team of manufacturer of your laptop brand.