UhClem

No. If you issue a write command, the card will write the data. Mostly. I see in version 9 of the specification a mention of cache. With a flush cache command that could take up to one second to complete. Yuck. So maybe use an older card to avoid...

Since those infrequent updates are too much for the supply, try decreasing the interval. More writes to the SD card but each one requires less energy. You might get lucky and find a rate which works.