Arduino Network causing severe battery drain on WiFi connected devices.

You'll understand if I blank out some of the IPs

Sure, didn't expect anything else.

So it's obviously bridged the relevant devices (giving br0). At this point I'm getting scared to bugger around with it

No reason to get scared. At this level (without saving anything) if anything goes wrong, just unplug your router from power and replug it, it will boot in a state as it was before.

We have to split the WLAN interface from the bridge. The command f

or this is:

brctl delif br0 <wlan-interface>

where stands for the name of the wireless interface. The command

iwconfig

should give you the list of your interfaces, all marked "no wireless extensions." are not of interest. You probably have only one with more information, that's your WiFi interface.

Before you split the bridge with the above command, issue the following command to activate ip forwarding (router functionality). Although this is probably already the case, it's just a precaution.

echo "1" > /proc/sys/net/ipv4/ip_forward

If you've done this, your WiFi interface should be in a separate segment. We still need to configure ip addresses and we have to check what netfilter rules are active.

To do all the commands be sure to use one of the ethernet ports on the router, do not use your WLAN for that, because that might be interrupted during the commands.

If you've done the above, please post the output of the following commands (again: changing public IPs to placeholders is perfectly viable):

ifconfig

iptables -L -n