Good battery management also depends a lot on your converter. The older Roadtreks (ours included) as well as many other older B's used the Magnetek single-stage charger which was a prehistoric beast if there ever was one. As many of the posters on this forum have done, we replaced the Magnetek with a Progressive Dynamics (PD9155 in our case) with Charge Wizard. This makes the world of difference for battery life, particularly if you leave the rig connected to shore power for extended periods. The Magnetek boils batteries dry if you leave it on like this, and it's a poorly regulated supply that requires the battery for filtering. The PD unit can operate with no battery if need be.
Having said that, we've had good results with the PD converter and inexpensive RV/Marine deep-cycle flooded cell batteries, e.g. Costco Kirkland. However, when the battery is no longer useable, I'm seriously considering putting two AGM's in the back of the under-bed storage area as they don't require venting. We can boondock easily for a couple of days now, but we'd like to extend it.
This coach has an Onan 2.8kw generator, so how long does it take to charge the aux battery?
The Onan Microlite 2800 puts out 23.3 amps. A 100 amp/hour battery usually should not be discharged more than about 80% (20% charge remaining). To charge 80 amp/hours with a 23.3 amp supply would theoretically take just under 3.5 hours.
However, it doesn't work that way.
First, different chargers supply differing amounts of voltage and current to the battery during the charge period. So the first variable is the charger used between the generator and the battery.
Second, as the battery becomes charged the internal resistance increases allowing less charging current to enter the battery. This is a non-linear function so it isn't easy to figgure out.
The short answer to you question is - it takes a long time for a generator putting out 23.3 amps to fully charge a depleted 100 amp/hour battery. I'm taking an educated guess at in excess of 24 hours.
The engine alternator, on the other hand, charges the battery directly without going through a charger - just like it does the start battery in the vehicle - and will, therefore, charge the house battery much faster.
The later in the season (and colder the clime) you camp / overnight without hook-ups in places where your generator use is limited by rules or courtesy, the more you need the 2nd battery. You'll be inside longer at night, thus more lights, TV, and computer use. And you'll use the furnace more. And batteries outside the heated space will put out less at lower temps.
The on-board generator (or an AC plug-in) will only charge the battery as fast as the converter allows... ie, pretty slowly for most B's. Running the engine is quicker, at least at road speed. RT's manuals used to have a comparison that was something like '10 hours of Onan vs 1 hour of driving', but I really don't recall it clearly. Alternator output varies quite a bit at idle, but is generally low.
Jim, "Horn broken. Watch for finger."
'06 Tiger CX 'C Minus' on a Silverado 2500HD 4x4, 8.1 & Allison ('Loafer's Glory'); '07 Forester 2.5 ( the 'HANDBSKT'); '95 Toyota SR5 V-6 4x4 pickup, ARB locker, Bilsteins, Warn hubs & M8000, etc;
'94 968, M030 swaybars ('DOPPLER')
Good battery management entails recharging at no lower than the 50% AH point. This is not feasible for some single battery people and it simply means the battery will need replacement more often.
Hence, a second battery will help with staying above that 50% point and you might get more than double the time to replacement.
You'll also get more of the full AH rating when you have heavier draws that exceed C/20.
Note that a leap to 4 batteries (>400 ah) is recommended if you want to add a 2000w inverter to give you a "household" ac circuit for anything you'd plug into your stick house.
If you don't mind running a gen you could skip the big bank but it sure is nice to not bring a gen for long weekends.
Dan
02 Freightliner Sprinter 2500 long tall home brew conversion
We have 2 100 amp-hr AGM batteries and no generator. We can go about 3 days before we see 50 % discharge.
Our 12V only compressor fridge is the biggest user of electricity (consumption is about 3 amps per hour while running and it runs about 40 % of the time - about 30 amp-hrs/day.) Lights run around 2 amps for each light - we mainly use 1 or 2 fluorescent fixtures. The fantastic fan takes 2-4 amps. The water pump uses minimal energy because it is on infrequently. The furnace fan must draw a fair amount but I don't know how much - we normally only have it on for short periods of time and never overnight. I don't know how much a TV draws because we don't have one. Surprisingly, our carbon monoxide and propane detectors together draw a total of 6 amp-hours a day.
This gives you a rough idea of our energy budget and may help you define yours. Just as a suggestion, I wouldn't let the purchase of a vehicle depend solely on such a minor point. As a second suggestion, if you do decide to add a 2nd battery I would seriously look at AGM's. Although they are expensive, they do not require venting like a regular lead-acid battery and that would make installation much simpler.
I don’t think I need a second battery. My van came with a 300 horsepower battery charger. It’s very quite and I use it to push the van down the highway when I am not camping.
Good battery management: Others will expand and modify this.
Turn off battery users when they aren't essential. Don't turn them on if you can do what you're doing without them. Know which things use the most juice and don't use them without knowing how much they will deplete your charge before the next opportunity to charge up. Don't run your batteries down too low. Good to have a monitor.
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