I needed a battery for my #D1 Mini UI Shield, so I revived this project and tried a second attempt. This time I'm using a bigger battery, LIR2450, though I made sure you can solder a holder for the smaller LIR2032 as well. There has been a change in how the charging works — with the switch on, the board is powered from the battery (through a shottky diode, to protect it from USB power you might have connected), with the switch off, the battery is charging.