Both cameras stopped working after battery replacement

Glad you attempted your own repair! Start by checking the connectors for both cameras. Always make sure to disconnect the battery. Its best to slide the guitar pick next to the battery connector, not directly under it as you can bend or damage the pins. Make sure they're free of debris and foreign objects. Also make sure they're not damaged or missing any pins. Once that is done make sure the connectors have a firm connection. They should snap into place like Legos. After you've confirmed they have a firm connection, you can test the device without fully assembling it. Just make sure you touch the glass and not the actual LCD to interface with the device. The digitizer is in the glass, not the LCD itself.