For Android and iPhone I recommend you consider Viewranger (the usual disclaimers apply - I have nothing to do with the company etc. etc.)
It’s specifically designed for phones and is not bad with battery usage.
It also has a useful facility called “Buddy Beacon”. As long as you have mobile coverage it will send your location to a central server at preset intervals - down to 30 seconds. You can allow “Buddys” to track where you are. If you lose coverage and then get it again later it catches up with the missing points. So it allows real time tracking.
£70 for the whole of the UK at 1:50K, £200 for the whole of the UK at £1:25K. Other countries available. You can download or for a bit more get them delivered on DVD.
The maps can be installed on 4 devices at the same time. They are big though!
You don’t need to use the premium (paid) mapping - there are other alternatives that can be downloaded.
The Buddy Beacon facility works without any paid mapping…
NOTE: Buddy beacon doesn’t replace the potential need for some type of emergency location equipment that works when you don’t have mobile signal. See other threads for discussion on PLB/Spot/Yellowbrick etc.