Hi @danielbernesdsd
Try replacing the batteries in the controller.
Here's the ifixit [guide|153860] guide that shows what to do.
Search online for [https://www.google.com/search?q=18650+battery+with+connectors&client=firefox-b-d&sca_esv=635483f0705dd420&sca_upv=1&ei=I5kUZqy2GI2I4-EPtey5iA4&ved=0ahUKEwjs09Ht_LOFAxUNxDgGHTV2DuEQ4dUDCBA&uact=5&oq=18650+battery+with+connectors&gs_lp=Egxnd3Mtd2l6LXNlcnAiHTE4NjUwIGJhdHRlcnkgd2l0aCBjb25uZWN0b3JzMgUQABiABDIGEAAYFhgeMgYQABgWGB4yBhAAGBYYHjIGEAAYFhgeMgYQABgWGB4yCxAAGIAEGIoFGIYDMgsQABiABBiKBRiGAzILEAAYgAQYigUYhgNI8R1Q5wVYrBxwAXgBkAEAmAH1AaAB3xaqAQYwLjEyLjO4AQPIAQD4AQGYAhCgAtoXwgIKEAAYRxjWBBiwA8ICDRAAGEcY1gQYyQMYsAPCAg4QABiABBiKBRiSAxiwA8ICDRAAGIAEGIoFGEMYsAPCAgoQABiABBiKBRhDwgINEAAYgAQYigUYQxjJA8ICCBAAGIAEGJIDwgILEAAYgAQYigUYkQKYAwCIBgGQBgqSBwYxLjEwLjWgB5Ve&sclient=gws-wiz-serp|18650 battery with connector] (supplier examples only) to find suppliers that suit you best.