Sorry, the battery has been built-in the tablet. We couldn't change. Eken company isn't like other well-known brand, like apple or Samsung. What they displays on their site are what they sell in the market. Eken F series tablets have the same CPU and similar hardware with flytouch series tablets. But flytouch has better battery. That's also the reason why Eken sold the cheaper tablets. If you want the tablets with 3600 mAh battery, we can order them for you from Eken. But the quantity requires above 50 or 100 with higher price.