Renogy 20/40 amp DC to DC battery charger (UPDATE)

I set this unit up as a super jumper? I had an old set of 4 AWG 20-foot real copper leads. I installed new parrot beak clamps and cut them at a 6' mark. I installed the charger. I used a fuse as the on/off switch. I hooked it up to a sulfated battery (voltage was 12.34 and had been set in the garage for 6 months) The "smart" charger went from 14.7 to 13.8 (float) in less than five minutes. So much for the "smart" charger eh? Then I hooked it up to one that was charged a few months ago. (Its voltage was 12.50) and it worked as it should. The nice thing is it has Lithium settings. You can set a single voltage from 12.6 to 14.6 (see the manual) It can also be used as a power supply. The unit has dual cooling fans (bad if you are in dusty conditions as I am while camping) So keep that in mind. It is now in a pelican case under the dinette. Oh, there is an error in the manual about setting up some of the Li settings. they are working on correcting. For the price at least for me was worth it.