@simonjb-
This is a Voice Remote that connects to the Roku via WiFi. Since the Roku itself has only a single WiFi radio, the Remote must find and use use the same Roku channel your Roku is tuned to for your local network - this is set on your WiFi router, not the Roku..
There is some evidence that one cause of battery drain for those with point-anywhere WiFi remotes can be your router using a channel that has a lot of interference from nearby routers using the same channel. This is more likely to be a problem in the more heavily used 2.4 GHz wifi band where it can also get interference from other sources like Bluetooth and microwave ovens than in the 5 GHz band.
If you have access to your router's setup, try configuring it to use a different WiFi channel to see if this helps the situation. If you are connecting in the crowded 2.4 GHz band, channels 1-11 are supported. Channels 1, 6, and 11 do not overlap each other and so give you the best chance at reducing congestion, so try each in succession, although depending on what channels your neighbors are using, other channels in the 1-11 range may work best. Also, reducing router bandwidth from 40 to 20 kHz may also reduce interference.
Note that optimum channel choice can be a moving target as neighbors bring new routers online in your vicinity, or reconfigure their routers to use different channels. I periodically use a WiFi analyzer app on my smart phone that can show me which available WiFi channels have the least congestion and I change the channel my router uses accordingly. I don't know if that explains my battery longevity (usually 3 months or more with fairly heavy use for my remotes with replaceable batteries) but it's probably worth a try to see if it helps.
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