I've got a small Mini Lite that currently has a single group 24 marine/deep cycle battery in it. Its got CA/CCA rating so I know it's not a true deep cycle. It claims 85AH on the label.
I'm in need of a new battery and I was looking at the Trojan SCS150. Now I'm wondering if just adding one of those is going to be quite enough? We'll sometimes boondock for 7 days. We do have a Honda EU2000 and we're pretty light on power use I'd say but there are some nights we need to run the furnace some. Should I be looking at adding another battery or will my generator keep the charge up with the single battery? I'd really hate to have to generate for hours on end to bring the battery to a full charge. Thanks.
What temperature ranges are you thinking? I was left high and dry by my battery one cold night near Tucson.
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Officially a SOB with a 2022 Jayco Precept 36C
Checkout my site for RVing tips, tricks, and info | Was a Fulltime Family for 5 years, now we're part-timing on long trips
The longer boondock trip that we do is usually in the fall and temps range from 40-60 on average. Last year we went a week earlier and it was 60-80, just an odd week I guess.
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Dan-Retired California Firefighter/EMT
Shawn-Musician/Entrepreneur/Wine Expert
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package
4pt Equal-i-zer WDH and 1828lbs of payload capacity
Two of those Trojan batteries that I mentioned earlier?
Two 12v or 6v deep cycle batteries.
Can't go wrong with Trojan batteries.
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Dan-Retired California Firefighter/EMT
Shawn-Musician/Entrepreneur/Wine Expert
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package
4pt Equal-i-zer WDH and 1828lbs of payload capacity
85 AH is a pretty good size 24 Dual Purpose battery. I have a pair of those in my camper and running the generator for 2 or 3 hours a day should replace what you use during the day.
Do not run the battery past the "good" light without recharging for 3 hours minimum.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
None of these recreational vehicles are equipped when purchased to spend that long away from shore power. Most owners don't boondock that much and the costs of extra batteries would be wasted on the average owner. Let's assume that you have 85 AH. Actually that means that you have about 40 or 45 that you can use without going below 50%, which works out to a little less than 2 amp hours average load for a 24 hour period. Not that much considering that your furnace blower will take at least 5 or 6 amps when running. Then you have water pumps, lights and the like.
For your usage you need two good deep cycle batteries, charger/converter that will put out enough current so that you can get back what you spend in a 24 hour period in a few hours of generator time.
If you install some sort of battery monitor (TriMetric or Victron) you will see that generator charging doesn't happen that fast. A nice 100 watt solar panel will give you hours of additional charging without the noise of the genny and actually mean that your discharge might not even start until after the sun sets.
1) The battery panel is not particularly useful to determine battery status while dry camping.
The top light (charging) will go out almost immediately after any load drops the "charger induced" surface voltage below approximately 12.7 volts (100% charged).
The "GOOD" light (and the other two below it) will stay on until the battery voltage drops to approximately 12.1 volts (50% remaining) at which point the battery should be recharged in order to preserve the maximum amount pf recharge cycles. If you walk by and notice only 2 lights on, you will most likely have reduced the useful life of the battery by the time you notice because unless you caught it JUST when the G light went out, you won't know the actual level of depletion.
BECAUSE the second to the bottom light is "FAIR" and will stay on until the battery voltage drops to approximately 11.6 volts (20% capacity remaining) which is dangerously low and permanent capacity reducing damage is occurring.
If you miss that one and see just the bottom light "LOW" lit you have waited too long and your battery is most likely dead (10.5 volts by definition). That light will remain illuminated until the battery voltage reaches 6 volts. That LED will NEVER go out unless the battery is removed or severely damaged internally (like frozen or shorted internally).
2) Only a battery management system like those mentioned (I use the Trimetric TM-2025RV) can give you an accurate battery voltage AND percent capacity remaining at a glance.
Not only that but it can actually display the Charge and Discharge CURRENT going into (amperage reads "minus") and out of (amperage reads positive) the battery(s). This will allow you to monitor the time to charge (so it is convenient to you) and the amount of generator run time before quiet hours you will need to get the battery to the point it will last through the night with the furnace running.
The Trimetric will also monitor the last time your batteries were equalized (in multi battery systems) and can monitor two battery(s) or banks. If you have solar or an external generator you can wire it so the B2 lead monitors that source instead of a second battery.
The newer version (the 2030-RV) can also sound an alarm at a level you set so you won't be surprised by a lower percentage than you want when next check the display.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
So I'd say my current battery is ruined seeing I have run it down so no lights show on the display and our fridge has actually shutdown. That all happened in our learning curve phase of boondocking, I've got a little more of a handle on it now. I just don't want to ruin $370 worth of new batteries.
Is the key to charging correctly to get the batteries up to 100% every time?
On the other topic regarding a dedicated battery charger vs the onboard converter. I also had 2 zincs to contribute.
The converter is tasked with running the DC requirements of your camper FIRST and anything left over will be given to the battery (if needed - as determined by the electronics in your converter).
As an example, suppose you have a 55 amp converter and you are using 30 amps of DC power (not at all unlikely without LED lighting). That leaves 15 volts "available" to charge your battery. HOWEVER, the actual battery voltage will determine how much of that 15 amps actually "goes" to a partially discharged battery.
If the battery is less than 50% capacity (12.6 volts or so) the converter will be in BULK mode when it turns on and most likely the entire 15 amps will go to the battery. However once the battery goes above 12.6 volts, the converter will switch to ABSOBTION and the converter will REDUCE charging current to a trickle (2 - 5 amps) in order to not boil the battery while charging and "topping up".
It can take DAYS to completely recharge a deep cycle battery using the converter.
However an external dedicated battery charger (I use a "Ship'n Shore plugged into my generator's 120 volt duplex outlet; not the battery charger - if yours is equipped) will not care "much" about the charge rate as it will assume you are watching the battery for signs of excessive charging (venting and water level reduction due to heat).
I typically switch off the battery bank when using the dedicated charger so as not to backfeed the converter. Folks have said it won't hurt the converter, but I feel better safe than sorry.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
So I'd say my current battery is ruined seeing I have run it down so no lights show on the display and our fridge has actually shutdown. That all happened in our learning curve phase of boondocking, I've got a little more of a handle on it now. I just don't want to ruin $370 worth of new batteries.
Is the key to charging correctly to get the batteries up to 100% every time?
Charging every time to 100% will certainly give you all the "engineered in" charge recharge cycles. However, I am not so "fussy" about getting to 100% every time.
Truth be told I normally do not because it takes so darn long even with a dedicated charger.
The "secret," if there is one, is to never let the batteries go below 50%. so plan your generator charging time to get it as full "as possible" before quiet hours kick in. I also start charging at about 70% remaining and fill to about 90% (or more) before shutting off the generator and putting everything away for the night.
The chart below will give you some idea of the "charge/discharge" cycles you can expect based on the depth of discharge you normally use.
NOTE ALSO: ONE deep discharge "normally" won't "destroy" a battery; It WILL however do permanent damage to the ability of the battery to reach its full rated capacity.
For example your 75AH DC-24 battery may only have a capacity of 70AH after a single deeply discharged (below 11 volts) event.
Doing that a couple of times will guarantee you will be buying new ones before you should.
In the chart below, the bottom axis is "depth of discharge" and the vertical axis is "cycles expected from a new battery".
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
A question about charging a 2 battery bank of batteries with an external charger. What is the proper way to hook the charger up to charge both batteries evenly? I assume you charge both at once?
A question about charging a 2 battery bank of batteries with an external charger. What is the proper way to hook the charger up to charge both batteries evenly? I assume you charge both at once?
A properly wired battery bank will balance charge using the same connections as the converter.
Make sure the ground wire from the charger is on the correct terminal of the shunt so that the Trimetric computer properly annotates the charge going into the battery bank.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
Linear Mode
