There are a wide variety of online stores that sell 12 volt batteries. The online sites for Wal-Mart and Staples, along with Amazon, for example, each sell this product.
One could purchase mobility scooter batteries from SpinLife. Other online sites where one could purchase said batteries includes Amazon, Batteries Plus, and Battery Stuff.
Energizer Lithium batteries can be purchased from Walmart in store or online. One can also purchase Energizer Lithium batteries from Energizer's official website.
You can purchase a 12v LED online from the Amazon website. Once on the page, type "12v LED" into the search field at the top of the page and press enter to bring up the items.
You can purchase Roomba batteries and accessories at your local Bed Bath and Beyond. You can also purchase them online at Amazon and have them shipped to your house.
One can purchase batteries for cars from local car parts stores. One can also order them online, from a select few retailers. One could also purchase one from a vehicle junk yard.
If you have a local Batteries+Bulbs store, they have or can get them for you. They can also be ordered from many online stores.
One can purchase extra motorola radio batteries at electronics stores, possibly at Radio Shack or at Best Buy. It would also be possible to purchase such a battery online.
You can purchase 12v heater from your local retail chains such as Walmart, Target, and Sears. You can also purchase one online and have it shipped to your house from websites such as Camping World and RV Plus.
Four 12V batteries may not be connected end to end to obtain 36 Volts. But four 12V batteries can be connected end to end to provide 48V and push 36 amps. The actual answer to your question suggests that you drop one 12V battery and use three, not four 12V batteries end to end to obtain 36V.
You can purchase power one batteries either online from Amazon, or from an electronics store that is close to where you live. You could also go to Wal-Mart.
There are actually a number of places one can purchase AA lithium batteries online. I would recommend Battery Plus and Amazon for starters. You can also try retailer websites like CVS and Drugstore.com
A Uniross charger holds 2-4 batteries. You can purchase a Uniross charger online from retailers such as Amazon. Alternatively, you can purchase one from eBay or Craigslist.