“Portable” auxiliary battery system

gatorgrizz27

Active member
Hi all,

I recently purchased a Land Rover LR3 and have been getting it setup as a DD/camping vehicle. For a couple reasons, I’ve been looking at adding an auxiliary battery setup, but believe a portable setup would be more versatile for my needs.

#1 is a winch. I plan to build a 2” front receiver hitch to accept a multi-mount winch and run leads with a quick connect to the main battery. For general off-road use, this is where it would live. However, it would be nice to do a single rear recovery or two, given that the mounting hardware already exists.

The auxiliary battery in a box would power this, as well as being a portable solution to bring along on the wife’s Range Rover for a ski trip, etc. The winch will also be used on my open utility trailer which will require it’s own battery, and eventually on my Range Rover Classic. Bunch of birds stoned with one winch + battery.

#2 is a fridge if I eventually go that route. I don’t want one permanently mounted, so having to carry the battery when I wanted it to run overnight wouldn’t be a big deal. Basically, I’d power the fridge off the main battery when driving during the day and charge the aux battery, then unplug and swap over to it at night when camping. Not a big deal when you’re moving daily, and again allows it to be used on multiple vehicles. If the charging circuit could keep up during the day, I might not even need to switch back and forth.

To charge this battery, as well as keep my cargo trailer/camper batteries topped off (not at the same time), I’d run an 8-10 gauge wire to the rear of the vehicle with a 60A connector. Would this Blue Sea ACR work to power up this circuit only when the engine is running?


I use these plugs for my boat trolling motor battery and charger, so building a male pigtail would allow me to charge the auxiliary battery with that charger also.


On the battery box I’d also have an Anderson connector for the winch, as well as a fridge plug and 12v socket.

Thanks for any input, I’ll try to add a drawing later to make things more clear.
 
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Photobug

Well-known member
It sounds like a feasible plan until you factor in the winch. I don't know much about winches but think it is a high amp draw item, I am going off of a windlass on a sailboat. You don't operate a windlass without the motor running. I would think you would want the alternator's help while using the winch, which means you will have to wire both vehicles to the battery and winch location. It starts to get complicated and expensive.

Powering the fridge and other things from a portable battery pack is a reasonable plan, I am building one now. One thing to consider the weight of a battery. Lead acid is heavy to to get near 100 AH you are looking at a 50+ lb battery plus all the other things you box needs. Liking to keep the box under 50 lbs I am looking at a Lithium batteries which are less than half that weight. Now your talking $1000+ battery and all the things needing to support a lithium battery. With the right setup (charger, etc) a lithium is more efficient and you could get by with a lesser AH battery as long as you are not trying to power a winch.
 

gatorgrizz27

Active member
It sounds like a feasible plan until you factor in the winch. I don't know much about winches but think it is a high amp draw item, I am going off of a windlass on a sailboat. You don't operate a windlass without the motor running. I would think you would want the alternator's help while using the winch, which means you will have to wire both vehicles to the battery and winch location. It starts to get complicated and expensive.

Powering the fridge and other things from a portable battery pack is a reasonable plan, I am building one now. One thing to consider the weight of a battery. Lead acid is heavy to to get near 100 AH you are looking at a 50+ lb battery plus all the other things you box needs. Liking to keep the box under 50 lbs I am looking at a Lithium batteries which are less than half that weight. Now your talking $1000+ battery and all the things needing to support a lithium battery. With the right setup (charger, etc) a lithium is more efficient and you could get by with a lesser AH battery as long as you are not trying to power a winch.
Thanks, yeah I agree the winch would draw it down quickly. I’m thinking I would get one solid rear pull out of it on the LR3 or my wife’s RR in an “emergency” type situation. For general off-road use it would be front mounted and powered by the main battery with the engine running.

For using it on the trailer, I’m not sure how many pulls I would get, it would be loading things like logs or a broken down ATV. The amp draw increases significantly as the weight goes up, so if it’s not working that hard it shouldn’t be terrible.

I’m ok with the weight of it, I’d probably use a group 27 deep cycle battery which is what I have in my boat. It would basically be carried from the garage into the back of a vehicle and left there, not something I’d plan on carrying into a hike in campsite to power electronics.
 

john61ct

Adventurer
The alternators (or a genset + big charger) must be running in order to support winching level loads.

Battery is just acting as a buffer, unless a very large LFP bank.
 

Photobug

Well-known member
Thanks, yeah I agree the winch would draw it down quickly. I’m thinking I would get one solid rear pull out of it on the LR3 or my wife’s RR in an “emergency” type situation. For general off-road use it would be front mounted and powered by the main battery with the engine running.

For using it on the trailer, I’m not sure how many pulls I would get, it would be loading things like logs or a broken down ATV. The amp draw increases significantly as the weight goes up, so if it’s not working that hard it shouldn’t be terrible.

I’m ok with the weight of it, I’d probably use a group 27 deep cycle battery which is what I have in my boat. It would basically be carried from the garage into the back of a vehicle and left there, not something I’d plan on carrying into a hike in campsite to power electronics.
The concern with the winch is only getting half a pull out of it. Most batteries capacity is based on a 20 hour draw down if you have a huge amp draw you could drain and ruin the battery and not get out of the snow drift. If you are going with a 27 series there are already premade boxes to hold this with some connections already in place, made for trolling motors.
 

john61ct

Adventurer
True deep cycle batteries are very specialist units, not sold in big box or automotive channels.

For that sort of usage I recommend Oddysey PC-2150, G-31 size.
 

john61ct

Adventurer
That's how much high Ah capacity in true deep cycling lead weighs!

Reduce the loads you intend to service if you want portability.

Or go to LFP at over five time the price per Ah to save half the weight.
 

gatorgrizz27

Active member
Thanks, I’ve been doing some reading on running the winch directly off a battery and it seems to work fine for short pulls. Again, this would be very light duty stuff, where tugging the vehicle 5’-10’ back will free it, and you can drive out the way you came.

I’ll probably run one of the Interstate marine deep cycle batteries, I might bump up to the group 31 size. I don’t really care about weight, 80 lbs is a bag of cement and I’m not going to carry this thing out to the beach.

I have two questions related to the Blue Sea m-ACR I linked in the first post. Apparently it automatically connects based on reading the battery voltage (when the engine is running), and disconnects (when the engine is off). It’s not a true switched relay though like a continuous duty solenoid, so it might not work properly with the auxiliary battery disconnected.

I had planned to use this relay to isolate my accessory fuse block under the dash, so it would only allow things to be turned on with the engine running, but it might not work for this purpose.

The second is related to the charging rate from the alternator when it is plugged in. With a run of 8 awg wire, it can handle 50 amps, but is there a chance it could see more than that if the battery is deeply discharged and plugged in? I don’t want to overload the wiring, but I’m not sure how to throttle it besides a circuit breaker that would prevent it from charging all together.

The alternator will not be the main source of charging the battery, I’ll use a marine charger on it at home.
 
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