Arduino for STM32

Hi all I made a custom board based on STM32L052C8T6 with a 32.768Khz crystal (ABS05-32.768kHz-T) and 2x15pF caps. I uploaded simpleRTCAlarm example that fires an alarm every 60 second. If i use the LSI every alarm fires around 58 seconds (measured with my stopwatch). But if i use the LSE every alarm...

Thanks GonzoG for your reply. Question 1: Damn... you're right, i'll have to check it better for USB DFU bootloader capabilities. Or stick to upload by serial, that will always work, right? Question 2: Ok, so i'll include both crystals on my design and populate as needed. With custom Arduino boards ...

Hi all I'm a experienced arduino maker trying to enter the STM32 world. I made a prototype with a STM32F103 bluepill and a Lora SX1276 module and now i would like to design a custom board. My requisites are: - battery powered, most of the time sleeping - wake each hour to send data from sensors (RTC...