Where can you purchase a replacement battery for the Jam Classic?

You do not need the battery. Instead try to get the portable charger which is eventually less expensive than replacing batteries. This short link to purchase this product is here: http://amzn.to/1f7rUGz

If your model is different from what the page shows, check corresponding models below the product and you will find what you are looking for.

Hope it helps.

Picked up a 3.7 volt 500 mh LI-PO battery and fixed mine. The original battery is 40mm x 30mm x 5mm and part number VLP053040AH.

The replacement I purchased off eBay Part number 403040 it is 40mm x 30mm x 4 mm seller ‘eelectronicparts’.

You have to desolder the old and resolder the new.