Update luther's layout organize a bit with a diameter between 16-19 mm: https://www.keyelco.com/product.cfm/product_id/826 Keystone #500, CR1220 battery holder, Memory Protection Devices P/N BC12AAPC, http://www.memoryprotectiondevices.com/datasheets/BC12AAPC-datasheet.pdf BC2003 CR2032 2032 Battery Holder BH-331P Battery Type 3xAAA Keystone type.