Originally Posted by Farzad_K

Hello.

Before saying "this has been discussed a million miles" let me tell you that it has not. I am not looking for the hardcore dual battery system and involvement of the alternator, thousands of dollars by other-than-dealer shops. Nope, I am looking to have the second battery, a gentle, deep cycle 12v AGM or LiFePO sitting inside the 4R powering my 12v cooler BUT while being charged off the 12v 10A accessory port of the T4 at the same time while I am driving. I could do this using the built-in inverter but then I have to carry the 120v charging brick with me and they usually don't have the power to charge and to power at the same time, I don't think.

I have looked at a few options, Victron Orion Tr, DC-DC chargers for example, and similar Renogy devices. But neither one of them tells me if I can plug it into the 12v accessory port and charge a 12v battery while the battery is powering the cooler and they all are thinking that the alternator will be involved. Victron especially has been all over the place with responses to my inquiry and some of their ideas are more contradictory than others.

On the occasions of my roadtrip it would be for astronomy, and I will have solar cells on my Prnisu charging my astronomy battery during the day, so I have also looked at devices that can do MPPT at the same time and just taking DC from a source other than PV and charging the 12v.

All that I want is to have a battery that can keep my cooler running while I stop many times during a roadtrip, especially at night and during breaks at rest stops.

Thanks a lot for any thoughts and suggestions.

Farzad