On Monday, 16 March 2020 13:15:18 CET Maksim Iushchenko wrote:
> Hello,
> I use batman-adv to create a mesh network and recently I faced an
> issue related to batman-adv gateways.

What are batman-adv gateways? Are you talking about the batman-adv gateway 
feature? This feature is only about IPv4 DHCP (broadcast) requests.

[...]
> Please, suggest me how can I distribute default route to all nodes in
> the mesh network in the case where nodes have static IPv6-addresses
> (and also it is necessary to maintain the actual default gateway on
> the nodes). 

This has nothing to do with batman-adv. Sounds more like IPv6 router 
advertisement.

Kind regards,
	Sven