Xbox One S controller draining after board replacement

I replaced the board inside my Xbox One S controller (model 1708) with one ordered from iFixit, due to the sync button breaking on the original board. I did not unsolder any connections during the process and left the controller as I saw it originally. I checked and the controller was working perfectly, every button, trigger, and stick inputting properly. I come back the next day to find it won't turn on. I checked the batteries with a multimeter and, while one read over 1.5V, the other was at 0.6. I've put two other sets of batteries (one identical to the first, Member's Mark brand, and the second were Duracell Quantum) and the exact same thing happened in both cases. What could be causing this sudden drain?