I drove down the coast this weekend for a long weekend, so 3 days of camping, and some amazing new places to fly. Sadly, I left the battery chargers sitting at home I have 5 batteries, and 3 of those are semi-dodgy DJI originals, that I already consider suspect and don't use a lot, or use with great caution, but had to risk it with them because I was going to need every battery I had and then some to get through 3 days. Then I remembered someone here mentioned that the smart charger is actually built into the battery, so the battery really only needs a source of power greater than 11.1v and it should charge. I decided the dodgiest of my old DJI batteries could be the Guinea Pig, and so I grabbed a length of wire, stripped the ends, and improvised 2 power leads off the car battery and shoved them into the battery's charging holes. Turned the battery "on" and it immediately started charging. It never seemed to actually "finish" charging, but once the 4 lights had flashed for long enough, I did a test flight, and it was showing 100% and seemed to discharge at a normal rate (got 15 minutes 44 seconds flight time to the 20% mark off it). In the end I did the same to all 3 DJI batteries and they all responded similarly, except one only ever showed 89% charged, and the other 97%, none of them went to 100% the way that first one did. But they all seemed to fly just fine, with reasonable flight times, and the usual expected speed of discharge. I can't say I'd advise making a habit of it, but if you're ever really really stuck and HAVE to charge a battery without a charger, you could try shoving 12 volts into it (place the "positive" into the left side hole, and "negative" into the right side hole) and turn the battery on.