Genesis batteries - lets do some math

[chorky]

So, the only way I know to be precise is to run numbers, and engineer things. Throwing something together saying 'that'll be ok' isn't sufficient. it always causes problems. That being said - I have some questions regarding the genesis dual battery setup. To my knowledge, it is designed to 1) remove the factory tiny battery that causes people problems, and 2) provide a second 'aux' battery for whatever you want to hook it to.

I have seen a lot of folks talk about using that secondary battery as the 'house' battery to run things when parked and camping for the night. But, when figuring some numbers years ago over on expedition portal I kept coming up with problems, that didn't seem to have a great resolution other than 'more batteries'

So this thread has 2 intentions. 1) to hear from those who are actively using the genesis setup and are using that second battery as a 'house' battery to see their experiences, and 2) to run some numbers and get input from the group to see if maybe my math is wrong. I know electrical - but by no means am an electrical engineer....

The Fullriver Group 25 batteries advertised to be used with the Genesis kit are rated (listed right on the battery) as having 64ah of charge. Since these are AGM batteries, one never wants to go below 80% SOC to prevent damage. So 80% of 64ah nets you a use capacity of 12.8 ah of use before needing to be recharged.

A 'typical' fridge, ARB Zero 73 qt dual zone, is rated as consuming 2.9ah (I am unsure what the 'startup' amp draw is, which is a critical factor)

So by the math, 12.8 ah of capacity divided by 2.9 ah of use nets 4.41 hours of use until the battery needs to be recharged before damage takes place. However, based on my personal experience with golf cart batteries running my SnoMaster fridge, the batteries never even get down to 80% because the start up amp draw pulls the low voltage cutoff below the 10v mark which turns off the fridge automatically. So in my experience, 15% of a battery is the maximum that has ever been able to be used, which is 5% less than the recommended 80% SOC. Now this example is with the specs of the ARB Zero 73 qt fridge running purely on battery power with no other load or charging. This also DOES NOT factor in voltage drop due to wires, connectors, start-up voltage, etc....

Here is where I get confused. Genesis publicly states on their own site they 'average' that the second battery can run a fridge for 'typically 2-3 days'. This makes zero sense - or rather does not expand on any details. Lets assume that between the time you get to a camp site, and the time you start the engine the next morning, 10 hours elapse. With fridge use ONLY this would consume 29 amps. 29 amps is 45.3% of the batteries 64ah capacity, meaning you dropped the battery down to 54.7% SOC. At this percentage, the battery is now permanently damaged.

So - how is anyone actually doing this without replacing batteries every weekend? It does not add up no matter how you do the math. And it makes me question the point of the genesis system (aside from just removing the tiny motorcycle factory battery). Maybe the point of the system is NOT to have a house battery for accessories, but to rather eliminate the factory second battery and to make battery changes easier? This would make significantly more sense. However, then a house battery, or Jackery or GoalZero or something similar would still be necessary for camping needs (fridge, lights, etc...).

So, curious to hear how those who have this system are actually using it and what real world experiences are showing. Please provide specific details. Such as if you have solar, how much, how often it runs, how many hours you are using XX items with the engine off and if solar is still providing charge or not, etc.....

Thanks.

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[Dunks001]

Did the math on consumption and cost. Bought a solar generator from Goal Zero. Way less headaches.

 

[Plywood]

Umm……….use a deep cycle

 

[Mr._Bill]

Your math is no good unless you are using accurate numbers. After the fridge is cooled down and full, the draw is very low. Many get a portable power pack for the fridge, as they don’t have a second battery to run accessories, and can run it for several days. Cooling the fridge before use makes a big difference.

The Genesis system replaces the two odd size batteries with two equal sized. It adds a Smart Isolator to keep the starting battery from getting discharged. It is not good to run the battery too low, but doing so doesn't mean instant and irreparable damage.

The Genesis system is a good option for many people. Others add a separate battery system based on their needs. I left the factory system intact and added a Smart Isolator and a deep cycle battery.

 

[PsyRN]

The Genesis system is a good option for many people. Others add a separate battery system based on their needs. I left the factory system intact and added a Smart Isolator and a deep cycle battery.

I was thinking of something like this recently. Instead of reconfiguring the engine bay with another battery, why not just add a second battery in the bed? I'm getting a pop-up camper, so it wouldn't be out in the open. I just don't know how this would be set-up with keeping the aux battery. I know virtually nothing about doing electrical stuff.

 

[Mr._Bill]

I was thinking of something like this recently. Instead of reconfiguring the engine bay with another battery, why not just add a second battery in the bed? I'm getting a pop-up camper, so it wouldn't be out in the open. I just don't know how this would be set-up with keeping the aux battery. I know virtually nothing about doing electrical stuff.

The factory batteries and wiring stay intact. There is just a cable running from the positive post on the main battery to the smart isolator, same as connecting a winch or any other high-draw accessory. The isolator allows the engine to charge the remote battery, but separates them when the truck is off so the starting battery does not get discharged.

 

[chorky]

Your math is no good unless you are using accurate numbers. After the fridge is cooled down and full, the draw is very low. Many get a portable power pack for the fridge, as they don’t have a second battery to run accessories, and can run it for several days. Cooling the fridge before use makes a big difference.

The Genesis system replaces the two odd size batteries with two equal sized. It adds a Smart Isolator to keep the starting battery from getting discharged. It is not good to run the battery too low, but doing so doesn't mean instant and irreparable damage.

The Genesis system is a good option for many people. Others add a separate battery system based on their needs. I left the factory system intact and added a Smart Isolator and a deep cycle battery.

In this case my math is valid though. I have specifications directly from manufacturers. I have tested even my snomaster fridge - when pre-cooled, it draws 7 amps to start up the compressor for a few seconds, and settles around 3 amps. usually runs 10-30% of every hour depending on outside ambient temps

My current thought is the genesis system is good for infrequent heavy draws from a winch, as well as removing the factory motorcycle style aux battery with a larger easier to change one. But for actual camping, I cannot see how this system is appropriate to use at all - but it seems to be advertised that way.

I was thinking of something like this recently. Instead of reconfiguring the engine bay with another battery, why not just add a second battery in the bed? I'm getting a pop-up camper, so it wouldn't be out in the open. I just don't know how this would be set-up with keeping the aux battery. I know virtually nothing about doing electrical stuff.

For your situation it would be good to have a DC/DC charger. it will pull up to 30a of power from your charging system (connects to the main battery) and then it charges what is commonly called a 'house' battery. The house battery is specifically to run the electronics in your camper. The DC/DC charger can tie into the main battery under the hood and has no impact on the little tiny aux battery of these trucks. It is a parallel system but totally separate from the main system. The only implication is that it can pull up to 30a (depending on your charger size) of power which might prevent your truck from entering into ESS mode. Also by doing this route, you can get a LiPo battery or similar which are significantly lighter, and can be drawn down much further than a AGM battery without damage. They also hold more 'juice' essentially, and overall are better suited to a camper's needs based on their design type. The downfall of them is they are very expensive, they do not like cold temperatures at all, and they are not the most robust batteries (so flying down a dirt road riddled with potholes and washboards will kill it much quicker than it would kill a AGM style battery). It would be good for you to go check out the electrical section of Expedition Portal - there is a ton of amazing knowledge over there and that probably better suits your needs - at least for the camper situation.

 

[CJXJJT]

I would imagine, like my dometic the arb is only drawing 2.9 amps when compressor is on and that is only a fraction of the time the fridge is used. Also you should be able to use 50% of your total amp hour capacity without damage to your battery. The genesis system seems ideal for the winch, hi cap air compressor, a moderate sized fridge and jump starting your main battery in an emergency. The deep cycle battery doesn't have the cold cranking amps to properly help you in an emergency start.
I use a DC DC smart charger for my lithium 100 amp deep cycle house battery in my camper.

 

[LostWoods]

Since these are AGM batteries, one never wants to go below 80% SOC to prevent damage. So 80% of 64ah nets you a use capacity of 12.8 ah of use before needing to be recharged.

There's part of your problem, you have this concept backwards. AGM is good for an 80% discharge, not state of charge. The general recommendation is 50% for normal use but you can go deeper at the cost of fewer cycles before it loses capacity. It's still going to be a few hundred cycles even if you killed 3/4 of the capacity every time so unless this is something you're doing daily, it's not really something to worry about.

https://www.odysseybatteries.com/odyssey/docs/us-ody-tm.pdf

As was said above you need real world data to calculate load but the dude I knew with the Genesis/Odyssey setup in his Tacoma never had an issue with the house battery going flat any time we went out despite a massive fridge and camp lights.

 

[Mister Lamb]

Is Genesis' claim of running a refrigerator for 3 days possible? Probably. Will you need a battery replacement much sooner than someone not running a refrigerator off their car battery? Definitely.

I'm on the boat where I'm willing to accept a little battery degradation to be able to run equipment I normally wouldn't be able to run. Especially when in my case it would most definitely not be a daily occurrence.

Sometimes you just need to set the electrical calculations aside to be able to enjoy a cold one in the middle of no where...

 

[Imbuere]

I've always heard 50% discharge for AGM batteries. Even then, you're looking at tops of 40ah or so. This is pretty much why I think dual (under hood) battery setups are a thing of the past.

What you'll see going forward is a starter battery under the hood paired with a lifepo4 "house" battery in the cab. I built my lifepo4 battery from Chinese cells. 304AH for about $900. It weighs 47 lbs. An equivalent AGM would be like 450 lbs, nearly 10 times heavier.

Go a bit further out and you'll stary to see lithium titanite replace lead starter batteries. This will be great!

 

[Kevin_D]

You're reading the specification wrong.
64Ah is over a 20 hour period, at a constant draw of ~3¼A, it's not the absolute capacity of the battery.
So a refrigerator, with a low duty cycle, drawing ~3A, won't have any trouble running the presumed, "2-3 days."

Kevin

 

[Rummie]

All the theoretical numbers can make for fun internet debate. Bottom line is real world usage. I can tell you that I absolutely get 2 or 3 days of cooling on my fridge with a genesis system. My batteries are holding up great so far. I also run my Joolca and 12v fans. The only problem I have encountered was having the voltage get too low to seal the bags on my Wrappon Green toilet. Simple fix is to run the Jeep when you use it if the voltage is low or plug it into the Bluetti that runs the satellite dish.

Add in the replacement of the troublesome second battery and it is a win even if you have another electrical system on board.

 

[chorky]

Haven't ignored this thread, just haven't felt well last several days and can't seem to find the old threads over on expo portal that I was referencing.. Although I saw several over there also talk about 50% SOC for AGM. So maybe I'm thinking of something else. Still trying to find a particular thread I remember from a few years ago that had a lot of super in depth discussion.

Also heard word back from Genesis. They do in fact claim a straight up 64ah rating for the batteries. So the whole 20 hour rate thing - I have no clue what that is in reference to. I am more willing to bet they dont know and just sent back a response since the battery itself does say 64ah at 20 hour rate.

 

[chorky]

Finally got around to doing some updates. Figured it was necessary since the system and a fridge was ordered.

First, some tidbits. I called Fullriver to ask about the battery included in the Genesis kit. Unlike what I heard before, maybe there was miscommunication, it is 64 ah at a 20 hour rate. So that results in a total of 76.8 amps available. Notice this is total amps available. Their tech support group also recommended not going below 70% SOC. I know there are folks here and elsewhere that will debate that, but that is from their tech support so I am inclined to believe they should know what is best for their batteries. Here are a few screenshots of their graphs specifically for this battery if you care to see. (and yes, they said I am over thinking it as well, but to each their own and I want to be sure I don't have a "oops my battery died" half way through the night....)

You can see here that at 30% DOD - which is equal to 70% SOC, the lifecycles of that battery decline at an increasing rate. It seems to take another dive at about 40% DOD / 60% SOC. They did recommend against going below 70% SOC, so the 50% mark where a lot of folks suggest, is drastically reducing the lifecycle. That being said, 500 life cycles for a 30% SOC could quite well be 62 years (solely by the math) if one goes camping only 2 times a month for the 4 months or so of summer (of course we know that is not realistic at all). That being said, as the aux battery degrades, it will start to pull down the main battery with it even though there is a disconnect.


Anyway, ok so now that is straight, I wanted to get the specs of a fridge. Based on what a few others on this forum have said, and some videos and reading I have done, I settled on a Engle 45 combi. (https://engelcoolers.com/collections/powered-fridge-freezers/products/45-combi-portable-car-fridge) I chose this because it has the option of being a fridge/freezer, or just a freezer, or just a fridge. I also did a decent amount of poking around at their compressor and it is well above the competition, IMO. Many of their products are used in ambulances, and even organ transport (according to them of course). It also is a smaller footprint. I have a larger 67L snomaster in the basement being used as a second freezer, and it is much larger than what I truly need... 2-4 day trips is the reality of what I mostly will do, more likely is just an overnighter. So I pulled some data from them as well.

Unfortunately, this particular fridge only displays in C. There are 6 graphs here. 25 Celsius is 77 Fahrenheit. 35 C is 95 F. 5 C is 41 F and -5C is 23 F. I circled in red the 'position' my conditions are assumed to most likely to be in. You can see it is between 4 graphs, so some assumptions and interpolation had to be done to arrive at my estimated 0.94 amps per hour spec that was calculated. This is drastically different than the actual measured consumption of my snomaster which was closer to 3 or even 4 full amps per hour (it's also a 67L though).

So next I wanted to see, realistically, as in my original question to this thread, how long one could expect to run this fridge, and only this fridge, on the Fullriver Full Throttle group 25 battery (https://fullriverbattery.com/batteries/part-ft750-25/). So I plotted it out on a spreadsheet. The results, though not really surprising because I had some suspicions, are in fact humbling.

According to the math, with a full battery alone (no solar) this particular fridge with assumptions and estimations made should run, with the engine off, for 1.02 days (or 24 hours) until the battery has reached the 70% SOC point where the company recommends charging at. So, that's basically an afternoon of arriving at camp, sleeping, and a few hours in the morning before taking off - not terrible, but not desired either. So I extended it. I wanted to see what a more realistic number would be considering I do plan on adding a small RV style 12v water pump, instant water heater, maybe some lights, and maybe to charge my phone or something if I forgot to have it plugged in while driving.

As you can see, with all these things running, and plenty of estimations made, you get about 0.90 days (or 24 hours) out of the deal. Now that's sitting, camped out, no engine, no solar, just battery drain. Not bad really. Plenty enough for a nice fun weekend! (although recharge time is still of question!!!)

Now, seeing as how Genesis also offers a kit for the Diesel and 392 options, with a larger Group 31 battery https://fullriverbattery.com/batteries/part-ft1100-31st/), I wondered - now what would the potential stay be if I added that battery and connected it to the Group 25 under the hood. Could I go on a longer trip? Say, a 5-10 day trip with a veterans group local to my area? Well...maybe. those numbers come up to 2.43 days. So that entirely depends on how much 'sitting' is being done vs driving.

Adding solar to this, would of course extend all of those numbers depending on the particular solar parts, and quality/quantity of sunlight exposure (which is why I really enjoy Caltopo for trip planning).

So here is the full sheet. Check it out. Feel free to offer suggestions if you wish, or maybe this will just help out somebody else out there who like me is not satisfied with "it will be ok". I wanted the true specs, as close as I could get them without equipment and real world testing. This is important information to make sure that just 'hooking something up' doesn't either cause damage somewhere, cause something to just not work, or ruin a camping trip longed for or worse spending thousands on something that ends up not functioning and needing a few thousand more to make it work right. I found this interesting. Hope others do as well. You will have to do your own calculations and formulas though as I can't attach the whole file

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