Car charging (12V) a MacBook Pro 16" M1 (Take 2)

About 3 months ago (Dec 26, 2021), I posted a request for input regarding possible options for safely charging my MacBook Pro 16 M1, while sailing in the Bahamas and/or while traveling in my RV during the off-season (hurricane season).  In the following 3 months, I received two responses.  Both were incredibly condescending and totally inaccurate. Perhaps it was too much trouble to read the request. Or, maybe they were both too eager to rack up "points" for responding that they just threw a trash answer on the board, regardless of the quality (or lack thereof). Surprisingly, one was from an "expert" with a rating of "Level 10" and 112,351 points at the time. (This used to be such a great resource!)

The original post was here...

    Car charging (12V) a MacBook Pro 16" M1 - Apple Community

And the original inquiry was as follows...

I spend half of the year traveling in my RV and the other half sailing the "Out Islands" of the Bahamas. It's easy enough to find a place to find a 120v connection to charge my MBP16 M1 while in the RV, but it's a little less convenient to do so while in the totally 12v system of my boat. I can, of course use my 1500w pure sine inverter and the Apple MagSafe charge that comes with computer. But a direct 12v connection to a MagSafe is much more efficient and greatly preferred. I have such an adapter for my previous MacBooks with MagSafe 2, but not for the newest MagSafe on the 2021 MBP16 M1. 

I suppose I could use the inverter for fast charging and simply a USB-C port (with a 12v USB-C adapter) for maintaining a charge. But is anyone aware of a better option?

Thanks for any suggestions.

I'm confident that others might have a similar need for a correct answer. SoI thought I'd post a followup to that post to share my own findings. As it turns out, my suggestion that: "I suppose I could use the inverter for fast charging and simply a USB-C port (with a 12v USB-C adapter) for maintaining a charge" was indeed correct.

If I'm at a dock aboard my sailboat or in my RV at an RV park, I simply use the 120v hookups and simply charge with Apple's 140W MBP16 M1 "MagSafe" charger. It's seldom, however, that either of these conditions occur for myself. While cruising in my boat, I never stay at marinas, but always anchor out... "far from the madding crowd" as it were.  While traveling in my RV during the off-season, the same is true, as I'm typically "boon-docking" somewhere.

IN MY RV...

When the laptop is in need of a good charge, I simply use a quality 300W Pure Sine Inverter. Note that I have a permanently installed 2000W Pure Sine Inverter. But since all inverters waste some power in the process of conversion from 120v to 12v, I prefer to use a 300W for better efficiency... big enough but not overkill.  (Never use a non-Pure Sine inverter for this and also make sure that the one you use is of good quality!) 

I plug Apple's 140W charger (that came with the MBP16 M1) into the inverter, using a typical 12-V power outlet (similar to a cigarette lighter). This has over-volt protection and is suitably wired and fused. Since the RV's generator is charging both the coach bank and house bank while the under way, I can easily fast-charge the laptop without running down the batteries. While not underway, I simply plug a USB to USB-C cord into the above-mentioned 12-V power outlet, which will maintain the charge (fairly well), albeit not actively charge the laptop batteries. This works quite well, without draining the coach batteries.

WHILE SAILING...

I'm currently sailing now and the same solution is also working perfectly under these circumstances... with some minor differences. My boat has about 380W of solar aboard. On a sunny day at anchor or when under sail, therefore, I can recharge the batteries during the day. I can then maintain a charge at night with the aforementioned USB to USB-C cord, simply from the house bank. If I'm at anchor, or sailing without benefit of the engine running, I keep a very close watch on my battery status. If, during the night, the voltage approaches 12v (normally 12.3v or higher), I will start my inboard diesel engine and run it for about an hour. This is sufficient time to bring the charge back up on boat's house bank. During this time, I also use the Apple 140W charger to revive the MBP (if need be).

FOR OLDER MACBOOKS...

Older and/or smaller MBs likely will not require these methods. The 13" MBPs and Airs, for example, have a substantially lower power requirement. With my 2015 MBP15", I used a dedicated charger that is wired into my 12v system and which has a MagSafe II adapter. Unfortunately, it does not put out sufficient wattage to safely charge the MBP16 M1 MacBooks.

This has been an effective and safe way to maintain the laptop batteries while on either cruising to off-the-grid destinations in my boat or my RV. I hope this provides solutions to others in similar situations, as I have little doubt that there are many "in the same boat" (so to say).