Welcome @execchefmjm to our forum. I would suggest asking that kind of question in our noob thread. This thread is supposed to serve as a picture thread 
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To answer you, you can. You have to buy the same battery though and connect it parallel. Welcome btw.
They NEED to be the same voltage when you do that, or 
Easiest way is to charge one battery, then the other battery, with the same charger, all the way to green light. Then connect them together in parallel and don’t disconnect them.
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This^
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