I have this small converter I had purchased before converting my '46 to 12 volts. This is brand new, never used, Chinesium.
If you have a 6 volt Inline, which is very common for the majority of them, this will allow you to run a cigarette lighter so you can plug your phone in to either charge and get power while your using the maps.
They are not very expensive, I think I paid about $20-$25 for it, and if someone can use it you pay the shipping, which we're gonna call $10. This weighs 24oz and the largest an envelope can be mailed 1st class postage is 13 oz, so unfortunately the next cheapest is small flat rate priority, which is $8.25, so that's why I'm rounding it up to $10, I need to pack it and take it to the USPS.
If you're interested ping me and we can exchange info to get it to you and you can pay me as a PayPal gift for $10, easy-peazy.