not exactly, since rech. station allows you to charge something without removing a battery from your vehicle. (imagine mob base)
but it would be more efficient, i agree.
yes and no. when charging something with batteries, you gotta charge it with DC power of voltage a little higher than the rated one.
so to charge a 12V battery, you would need ~14V continually IIRC.
Now a veh battery provides 12V, so no problem there.
As for transformers and converters, the electrical system is super simplified as we all know. There is no voltage or amperage available, implying that all appliances and electrical parts work in the same voltage.
This is certainly unrealistic, but means that there will be no problems related to destroy internal parts of appliances.
well, the one possible problem with charging, is that it happens over time, not instantly. it could take hours to fully charge a battery.
I was thinking to solve this by checking every 5’ if the battery is around the item, and if it is, charge the item by a portion of its max_power, while discharge the battery of the same amount.
i imagine it as charging the flashlights batteries, not loading electricity. (can require to have a rechargeable battery mod attached, much like the rech. station)
also: it IS the future. i find it highly suspicious that not all small house appliances are not running off rechargeable batteries.
Benefit is not very great, but the change is not that hard to do too.
(without looking at the code) i was thiking it fairly easy to implement:
when one tries to reload an appliace the game checks for batteries in his inv.
(or if we talk about rech. batt. mods only, just alter the charging function)
So we can also check if there is a veh_battery + wire around and ask the player what he wants to use in the familiar menu.
If he chose veh_battery, discharge that battery by the amount loaded to the appliance over time.
PS. ok, regardless of what i think, i will not try to do that unless i get some positive opinions. 
