I've been following this thread out of curiosity.
I don't have a GPS thing I tend to write my directions as a road route plan, without the sophistication of Dakar etc. competitors,
but have on occasions needed GPS to get me to a specific location once close to target.
So my phone comes into play.
I don't like GPS as it limits my ability to see what the surrounding area is likely to be and when/if looking for a place to rough camp, gives no useful information as all the none road bits just show as a colour, whatever the terrain, so I've no idea if the area off to my side is suitable for throwing down a bivvy bag or not.
During COVID shut downs the only sensible manner for me to get from home to work was ride.
So my notes consisted of the following written via my computer and printed out of A4 paper and folded to go with my maps in the
map pocket on my tank bag.
For the approximately 2000 km journey the notes consisted of.
Four lines at point 12 font typing from Barcelona to French boarder.
Another 8 lines again at 12 Font type size to get from Southern French border to Northern French border with Germany.
Two and a half to two and three quarters of A4 pages notes, again at font size 12, to get from Southern German border to Bremerhaven.
What a ball ache.
When asking a German local how they navigate around their homeland, they stated without hesitation 'with GPS'.
Things that may help the battery issue.
Shutdown all programmes not in direct use.
Shutdown all update facilities of 'Apps'.
F*#<ing Apps are not going to save the planet or save you money but their constant need to 'refresh' will drain your battery.
Other things that may help.
I have a charge socket on my bike and run a lead up to my tank bag with a socket at the end for whatever I need to plug in.
I have a 2.2amp USB socket for emergencies there are higher amperage ones. See link below.
Only the charge socket is permanently attached to the bike so little opportunity for theft or water ingress when not in use.
Socket has cap to seal out water and is tucked away from easy sight and water, whether rain or wash down.
On other bikes I have an Optimate charge lead.
Optimate also do these.
https://optimate1.com/prod/usb/
Pick your preferred option.
The socket on my day to day mile muncher is a DIN ISO4165 (eg BMW socket type) Schaub connection, so the combination of plugs, sockets, extension lead etc give me plenty of options take up bugger all room and are not left on the bike so can't be nicked and or filled with water and most importantly of all, they run of the main battery of the bike with a nice big alternator and near 30 amp hour battery keeping everything sweet.
Hope this helps.