Recommended Multi-Battery and Smart Controller Charger

[Bbarr]

That step up transformer I posted earlier lets you get 13.8v even when parked. One does have to watch system voltage with those if they only have one battery. My truck has a dual battery setup, plus I also put in a third portable one in back that self-charges off the backup battery or solar panels when we are camping.

Please explain, Transformers do not work for DC ?