>>772539Germanbro here, you want Osmand for maps. The maps are Openstreetmap and in yirop very detailed. And they are free! You can even make your own, with only the route you plan to take, there are sites for that. It also has offline routing, which means you never need anything but GPS. Which, by itself, doesn't eat much power.
You can use Google offline but you can't route and its not reliable, sometimes you need to be online regardless.
For energy: Get a AA to USB emergency battery, Varta sells two kinds, i had both, they work flawlessly. 8 AA batterys can be bought for 2 euros or less at any supermarket.
Yes, bring a filter, search ebay for a sawyer mini that gets sent from the US, you will only pay 16 euros with shipping. 6l seems a lot. Not sure how often you plan to hit stores but asking people will get you water all the time, nobody will send you away. However, often people invite you for food and chatter, this can cost time.
