I'd have to go look at it, as I always leave it under the back seat of my truck. The trouble with Walmart is they often change brands depending on which Chinese junk vendor offers them the best price at any given time, so even if I told you the make and model, you probably couldn't find it. But it is a 400W model, and I have it wired direct to the battery (I have a 100A power distribution panel behind my back seat to run radios and other electrical gear).
As for charging, my flights are typically very short, about 3 minutes or so, and that only pulls about 10% out of a pack. And I follow the ABC rule: Always Be Charging. So after each flight, I put the packs on the charger (man, do I ever hate that **** artsy-fartsy thing - why couldn't they have designed a charger that is functional) and run them up to 100%. And for me, this typically takes about 10 minutes.
Now if I take a set up idle packs (that have self discharged), these are usually about 60%, and that will take about a half-hour, give or take.
Frankly, I think DJI does a horrid job with battery management and charging, or at least, it's nothing like what I learned as best practices for LiPo cells. But if all you want to do is make money, then of course you want your customers to burn through grossly overpriced batteries as quickly as possible, but I digress.
In any event, I don't think you need to spend a lot of money on a vehicular charging solution, but I suppose that depends on your needs. And if you have a newer vehicle (i.e. late model F150), a lot of those already have 400W 100V outlets in them, so no solution is needed.