VEVOR 12V 40A DC to DC Battery Charger, 500W, On-Board Battery Charger for Lead-Acid, Lithium, AGM, GEL, and Flooded Batteries, Smart Multi-Stage Charging, for RVs, Commercial Vehicles, Boats

Unit pulls upwards of 80 amps from a 13.5v source, the setup I have going is 2 GreenOE 12V 100Ah LiFePO4 in parallel (also from Walmart), in my camper, and I ran about 18 feet of 8 awg wire with a 50 amp circuit breaker by the truck battery (source) to this DC to dc charger in the battery well then about 2 feel for 8awg wire to the 2 LiFePO4 batterys (aux batteries) and a 50 amp circute breaker right by before the aux batteries, at first I thought it was a bad circut breaker by my truck batterie or maybe the wire was damaged so i was checking everything and couldnt find any issues so I went and got a 60A circut breaker thinkjing mabe it was hitting 50A and poping or the cirut breaker was bad, but still had the same issue so i went and god a amp meter. To my supprise the thing was pulling 75-80 amps on the source side at 13.5 volts by the time it got to the DC to DC charger and it was stepping it up to 14.6v at 40 amps, so its only working at about 50% eficentcy to boost ~1v... I think I'm going to return it, but it does work and does what it says it's going to do, but for the cost of re-wiring 18ft to 4 awg, it's actually cheaper to get a more efficient inverter, not to include the stress on my alternator and reduced MPG from the increased load.