Adding 2nd 12v Battery for Accessories

[thrukateyes]

I have the 2024 Hybrid. I'd like to add a second 12v battery with a disconnect to power a refrigerator for when the truck is turned off. I'm open to having it in the cab or bed (slight preference for cab access while on a long road trip). Can I wire off of the 12v battery in the backseat? Any better ideas or ways any of you have set yours up? Or did any of y'all go the battery and solar route for your rig? Cheers!

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[BrianA]

Have not done it in a mav, but have in other vehicles. Assume you have the inverter? I would not connect it to the vehicle battery at all or mess with 'wiring it in'. Just buy a battery and a separate small charger and plug it into the inverter. 400 watts should give you 25 amps of charge, maybe 20 (not sure how efficent the charger is). Maybe not as efficient to invert to 110 AC just to go back to DC and charge, but we are talking a few watts. It does require a second charger, but they are cheap and now you have it if you need for another vehicle. Biggest benefit of this route is it avoids any issues with the BMS, your auxillary battery discharging your vehicle battery, and has a lot less chance of ever leaving you stranded.

 

[wax87]

I would look at what the people do to convert their vans into a camper van. Lots of good info and drawing come from that community.

 

[RichardCranium]

What size battery are you planning to use? Some battery chargers don’t work well with the modified sine wave inverters. You could always get a dc to dc charger that isolates the 2 batteries.

 

[mav47]

@thrukateyes

You're looking for a setup not so different from our little camper: we have a 135Ah LiFePO4 battery in there, which is charged from the Maverick Hybrid, directly from the truck's own 12V AGM battery through a 30A fuse holder. Works great.

Your idea of adding a dedicated battery inside the truck for the fridge is great I think. I'd get a small (50-100Ah) LiFePO4 battery, one cost effective brand with generally good reviews is LiTime. You can mount it under the back seat in the storage compartment bin, measure which size would fit. I don't think you'd need much more than 50Ah anyway. But ABSOLUTELY install proper insulating covers for the battery terminals. You could consider placing that battery on its side in that plastic bin for safety. The biggest threat causing an instant fire is shorting those terminals or shorting the positive terminal to ground.

We want this battery charging ONLY when the truck is on. For that purpose I use a Victron Orion 12/12-18 DC-DC converter and its output will charge your new battery at a voltage you can set (I'd set it to 14.4V), and it will work with an input voltage between 8 and 17V (!!). I picked the power feed directly from the positive (+) terminal of the Maverick's battery, through a 30A fuse holder. This particular Orion unit has an output of 18A meaning that a 50Ah battery will take about 2 hours of driving to fully recharge. There's also a similar Orion 12/12-9 limited to 9A output (which is likely plenty for most, at roughly half the price).

Either Orion unit will fit on the rear cabin bulkhead behind the rear seat somewhere.

The Victron Orion has an external input wire you can connect an accessory +12V lead that turns on and off with the truck, so this will turn the DC-DC converter ON or OFF too.

As soon as you turn on the truck: the DC-DC converter will start charging the accessory battery. Any time the truck is off, the DC-DC converter shuts off, and then your accessory battery will be powering the fridge by itself.

If you don't want to fiddle with an external trigger wire, you can choose the (more expensive) Victron Orion 12/12-18 SMART. This unit is easily programmable over Bluetooth and it will monitor the input voltage from the truck and turn itself on and off accordingly. So if you set it to turn on at 12.8V, the output will turn on when you turn on the truck, and shut off within seconds of you turning off the truck, and you'd set the output to something like 14.4V.

There are likely DC-DC converters from other brands with similar suitable functionality, I'm just not familiar with those.

With either DC-DC converter:

The Maverick BMS will choose an onboard voltage in the truck between 13V (not charging the 12V battery) and up to 15.2+V (fully charging), and that means that your DC-DC charger will be charging your accessory battery at any time, irrespective of the truck BMS. Even at 13V in the truck it will still charge your accessory battery at 14.4V.

MAKE SURE you put a 30A fuse holder on a 10AWG wire from the Maverick battery to the Orion, and another 30A fuse on its own 10AWG wire output to your accessory battery. These fuses MUST be located close to either battery!

The wire from your accessory battery to the fridge is likely smaller gauge and you'd want to fuse that separately with a suitable value (like 15A for a 14 AWG wire). I would probably add a dedicated 12V socket below the rear seat that you can plug your fridge into.

FUSE wires APPROPRIATELY, make proper wire connections, & all that jazz. The above writing is simply my opinion, use your own good judgement.

Cheers!

 

[Pstewone]

Mav47,
Thank you for the great post! This is what I am looking to do to charge my 100ah lifepo4 with my Victron Orion 12-12 /18amp charger. I used this charger / battery setup on my older non-hybrid SUV to power my 12v refrigerator/cooler and it worked very well. I have a 2025 AWD hybrid. Is it posable for you to send me some pictures of your work and where you mounted the charger etc.? Question: do you have any issue with the charger cycling off and on when the hybrid goes into electric mode? My guess is you can control that with the setting on the Victron application but had to ask.

I look forward to your reply.

 

[Pstewone]

@thrukateyes

You're looking for a setup not so different from our little camper: we have a 135Ah LiFePO4 battery in there, which is charged from the Maverick Hybrid, directly from the truck's own 12V AGM battery through a 30A fuse holder. Works great.

Your idea of adding a dedicated battery inside the truck for the fridge is great I think. I'd get a small (50-100Ah) LiFePO4 battery, one cost effective brand with generally good reviews is LiTime. You can mount it under the back seat in the storage compartment bin, measure which size would fit. I don't think you'd need much more than 50Ah anyway. But ABSOLUTELY install proper insulating covers for the battery terminals. You could consider placing that battery on its side in that plastic bin for safety. The biggest threat causing an instant fire is shorting those terminals or shorting the positive terminal to ground.

We want this battery charging ONLY when the truck is on. For that purpose I use a Victron Orion 12/12-18 DC-DC converter and its output will charge your new battery at a voltage you can set (I'd set it to 14.4V), and it will work with an input voltage between 8 and 17V (!!). I picked the power feed directly from the positive (+) terminal of the Maverick's battery, through a 30A fuse holder. This particular Orion unit has an output of 18A meaning that a 50Ah battery will take about 2 hours of driving to fully recharge. There's also a similar Orion 12/12-9 limited to 9A output (which is likely plenty for most, at roughly half the price).

Either Orion unit will fit on the rear cabin bulkhead behind the rear seat somewhere.

The Victron Orion has an external input wire you can connect an accessory +12V lead that turns on and off with the truck, so this will turn the DC-DC converter ON or OFF too.

As soon as you turn on the truck: the DC-DC converter will start charging the accessory battery. Any time the truck is off, the DC-DC converter shuts off, and then your accessory battery will be powering the fridge by itself.

If you don't want to fiddle with an external trigger wire, you can choose the (more expensive) Victron Orion 12/12-18 SMART. This unit is easily programmable over Bluetooth and it will monitor the input voltage from the truck and turn itself on and off accordingly. So if you set it to turn on at 12.8V, the output will turn on when you turn on the truck, and shut off within seconds of you turning off the truck, and you'd set the output to something like 14.4V.

There are likely DC-DC converters from other brands with similar suitable functionality, I'm just not familiar with those.

With either DC-DC converter:

The Maverick BMS will choose an onboard voltage in the truck between 13V (not charging the 12V battery) and up to 15.2+V (fully charging), and that means that your DC-DC charger will be charging your accessory battery at any time, irrespective of the truck BMS. Even at 13V in the truck it will still charge your accessory battery at 14.4V.

MAKE SURE you put a 30A fuse holder on a 10AWG wire from the Maverick battery to the Orion, and another 30A fuse on its own 10AWG wire output to your accessory battery. These fuses MUST be located close to either battery!

The wire from your accessory battery to the fridge is likely smaller gauge and you'd want to fuse that separately with a suitable value (like 15A for a 14 AWG wire). I would probably add a dedicated 12V socket below the rear seat that you can plug your fridge into.

FUSE wires APPROPRIATELY, make proper wire connections, & all that jazz. The above writing is simply my opinion, use your own good judgement.

Cheers!

Mav47,
Thank you for the great post! This is what I am looking to do to charge my 100ah lifepo4 with my Victron Orion 12-12 /18amp charger. I used this charger / battery setup on my older non-hybrid SUV to power my 12v refrigerator/cooler and it worked very well. I have a 2025 AWD hybrid. Is it posable for you to send me some pictures of your work and where you mounted the charger etc.? Question: do you have any issue with the charger cycling off and on when the hybrid goes into electric mode? My guess is you can control that with the setting on the Victron application but had to ask.

I look forward to your reply.
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[mav47]

@Pstewone

That Orion DC-DC charger in our little camp trailer is the non-smart one, so I have to turn it on and off somehow.

Originally, I had added a voltage sensing circuit ($6 on Amazon!) that has a relay output and that you could set to a certain "RELAY ON" voltage, and then another (lower) "RELAY OFF" voltage and this relay turned the Orion ON and OFF. What I encountered was some occasional instability, with the relay ending up in a "buzzing" state. No bueno.

My guess is that with the "smart" version of said Orion you'll have much better control, as it has this voltage sensing ON/OFF functionality built in.

Note that the Maverick will provide DC system voltage between 13V and 15.4V, depending on the state of charge of your 12V battery in the truck. So you'd have to set the Victron Orion to turn on at say 13.5V or so, and turn off at say 12.6V.

Since I already had the non-smart Orion, and since I'm actually "behind" the 7-pin trailer plug (my Orion and my 400Ah LiFePO4 battery are both in the camp trailer) I decided to use the DRL light wire going to the taillights to turn my Orion on and off. The power feed for the Orion comes from the continuous +12V line on the 7-pin, which is fused from the Maverick's battery with a 30A fuse. Pretty simple!

I have my Orion charging output voltage set to 14.2V, so that means that irrespective of the Maverick's onboard voltage, which can be between 13V and 15.4V, I'll have 14.2V going to the LiFePO4 battery, which I find to be about perfect (=3.55V/cell in that battery)

So that means that with the trailer connected as soon as I turn on the tail lights, the Orion turns on and provides charging output. If you park the truck/trailer combination, keep the trailer connected, then the Orion will shut off as soon as you shut off the truck lights, so the Orion doesn't drain the Maverick's 12V battery.

It is worth mentioning that I set the DRLs in the Maverick to include the taillights, and the DRLs are set to AUTO, so basically the taillights will always be on while driving day or night. That's a setting change you can make in Forscan. I do this for safety, and find it convenient with this Orion setup too.

I have a pretty large LiFePO4 battery, and have a 250W solar panel on the trailer's roof (with a Victron controller). But if we're camping in the shade for several days and I need some charging power to keep the fridge going, then I need to not only turn on the truck, but also turn on the lights. I find that to be fine.

In regards to your question: the Maverick's own onboard DC-DC charger is powered from the hIgh voltage battery, and its output is not related to EV mode or Hybrid mode.

Cheers!

 

[Pstewone]

@Pstewone

That Orion DC-DC charger in our little camp trailer is the non-smart one, so I have to turn it on and off somehow.

Originally, I had added a voltage sensing circuit ($6 on Amazon!) that has a relay output and that you could set to a certain "RELAY ON" voltage, and then another (lower) "RELAY OFF" voltage and this relay turned the Orion ON and OFF. What I encountered was some occasional instability, with the relay ending up in a "buzzing" state. No bueno.

My guess is that with the "smart" version of said Orion you'll have much better control, as it has this voltage sensing ON/OFF functionality built in.

Note that the Maverick will provide DC system voltage between 13V and 15.4V, depending on the state of charge of your 12V battery in the truck. So you'd have to set the Victron Orion to turn on at say 13.5V or so, and turn off at say 12.6V.

Since I already had the non-smart Orion, and since I'm actually "behind" the 7-pin trailer plug (my Orion and my 400Ah LiFePO4 battery are both in the camp trailer) I decided to use the DRL light wire going to the taillights to turn my Orion on and off. The power feed for the Orion comes from the continuous +12V line on the 7-pin, which is fused from the Maverick's battery with a 30A fuse. Pretty simple!

I have my Orion charging output voltage set to 14.2V, so that means that irrespective of the Maverick's onboard voltage, which can be between 13V and 15.4V, I'll have 14.2V going to the LiFePO4 battery, which I find to be about perfect (=3.55V/cell in that battery)

So that means that with the trailer connected as soon as I turn on the tail lights, the Orion turns on and provides charging output. If you park the truck/trailer combination, keep the trailer connected, then the Orion will shut off as soon as you shut off the truck lights, so the Orion doesn't drain the Maverick's 12V battery.

It is worth mentioning that I set the DRLs in the Maverick to include the taillights, and the DRLs are set to AUTO, so basically the taillights will always be on while driving day or night. That's a setting change you can make in Forscan. I do this for safety, and find it convenient with this Orion setup too.

I have a pretty large LiFePO4 battery, and have a 250W solar panel on the trailer's roof (with a Victron controller). But if we're camping in the shade for several days and I need some charging power to keep the fridge going, then I need to not only turn on the truck, but also turn on the lights. I find that to be fine.

In regards to your question: the Maverick's own onboard DC-DC charger is powered from the hIgh voltage battery, and its output is not related to EV mode or Hybrid mode.

Cheers!

MAV47,
Awesome detailed information, thank you. I do have the smart isolated Orion so that will save me some work. I liked how you solved that problem with the trailer lights. It's also a relief knowing "now" that the Maverick start battery is charged from the high-voltage battery. This gives me the convenance to move forward with my project.

Thank you again!

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