You'll have to plug in your external battery before turning on your R10 / DX100. Once you do that, R10 will automatically turn on and recognize your external battery as its main power source!
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FYI, Here I confirm that 256GB SD card in FAT32 format with SD to micro SD adapter work flawlessly with R10 / DX100. You can increase your R10's capacity up to 310GB!
I encourage moderator to add this to a main thread. This feature wasn't mentioned in R10 / DX100's manual.