Navigation

I use cycle.travel for route navigation on my iPhone but of course it drains the battery very quickly. I do download the base map, download the route and carry a power bank for backup but this is not ideal. Is it better to plan the route on this app but then send the route to a cycle computer with a long battery life for use on the ride? And if so, is there a simple, low cost computer you would recommend for this?

Many thanks

David