Canon WFT-R10A Wireless File Transmitter for EOS R5 C & R5 Mirrorless Camera - Manual (Page 173)

Battery Charging Order
You can select which battery to charge first, in consideration of the different purposes of
batteries on the left and right of the transmitter.
On the camera, press the 〈 〉 button and select [ : Battery charging ].
Select [ Camera first ] or [ WFT first ].
Caution
Any over-discharged batteries are charged first, regardless of the setting.
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