How to Keep Your RV or Motorhome Battery in Good Condition
RV Battery Care and Maintenance
As a retired engineer, I can hardly restrain myself from dropping into technical jargon and starting a lecture on the design of batteries, and cells, and charging systems, and so on.
But you can Google all of that specific information yourself in a thousand places on the web. So instead, in this section, I will try to provide some useful information on RVs and campers and their batteries and systems.
Coach Vs. Chassis Batteries
You should understand that almost all of your Class A, Class C, and in some cases Class B RV’s have utilized a dual 12-volt DC power system for years. Most of these systems contain 12-volt and 6-volt rechargeable lead-acid deep-discharge batteries (here's a slightly more technical discussion of "deep discharge").
These two systems of batteries (and their loads) are referred to as the chassis battery system and the coach battery system.
One system, the chassis system, is pretty much the same as a normal automobile electrical system, but is often (though not always) designed for higher currents (loads).
The other system, the coach system, generally provides the 12-volt DC power for everything in the RV coach.
Since fifth wheelers, travel trailers and even pop-ups are towed by another vehicle, they will just have the "coach" system. Newer models, especially, of these towed campers will have many of the same appliances as larger RVs.
Some Typical Battery Configurations
A pop-up camper or towed full-body camper might have one or two standard 12-volt deep-discharge batteries as coach batteries. These batteries generally get recharged when the camper is connected to the towing vehicle and the towing vehicle's motor is running. Or they may require being recharged separately.
Older (and smaller) RV's might have a single coach battery and a single chassis battery, each being a 12-volt battery.
The number and type of batteries in RVs have changed over the years to where it is pretty standard to have a "bank" of two 12-volt chassis batteries, and a "bank" of four 6-volt coach batteries wired in a 12-volt configuration.
Since DC electrical systems in coaches are 12-volt systems, typically two 6-volt coach batteries are wired in series to provide 12 volts. By using 6-volt batteries you can get a higher load capacity than by using 12-volt batteries in parallel.
Two batteries wired in parallel provide twice as much current capacity as one. Some RVs utilize four 6-volt batteries, and when wired properly, these four will provide more current than two 12-volt batteries.
These 6-volt batteries are usually the same as those used in electric golf carts.
Preventative Maintenance for Batteries
Remember, all your batteries require regular preventative maintenance.
Like many "full-timers" I recommend that you perform the following preventive maintenance, as a minimum, on a regular basis:
- Inspect your batteries and the whole battery compartment along with wiring that is visible. Remember your RV is bouncing over bumps and swaying around curves. A good thorough visual inspection before a trip, and after you set up at your campsite, can save you a lot of heartache later if you find such things as loose wires, frayed wires, a cracked battery case, spilled battery fluid, or battery acid build-up on your terminals.
- Before every trip, check all battery fluid levels and refill any cells that are low on fluid as necessary, with distilled water only.
- Before every trip, check that all battery connectors are tight, and are clean of any oxidation residue.
- When storing your RV for an extended time, check the batteries at least once a month and run your generator until they are fully charged. See the Table below for relative battery capacity.
- Remember, these electrical systems, even with the switches turned off, will leak low currents and this will, over time, discharge your batteries.
- When camping at a campground for an extended time, check the batteries at least every 2-4 weeks, especially the fluid levels in the coach batteries. Remember, these batteries are powering most of your lights and many appliance control systems, so even though you are plugged into 110-Volts AC at your site, they are constantly being re-charged and can lose fluids over time.
- Also, when camping for an extended time, start your coach engine at least every 30 days, and run it for at least 30 minutes to keep every thing lubricated in the engine system, but also to re-charge your chassis batteries.
Keep Your Chassis Battery Fresh
Once you have parked and set up your RV, turn the CHASSIS battery switch OFF (if you have one). That way the chassis batteries will remain fresh longer and be more likely to start your engine when you are ready to leave your campsite.
And you want to keep those chassis batteries fresh. Because when both switches are on, and you are not connected to 110-volt AC power—you know, boondocking, rough camping, whatever you want to call it—your 12-volt accessories are pulling power from all of your batteries including the chassis batteries.
It is very embarrassing to get ready to pull out at a campsite, and find out you don’t have enough juice to turn over your engine, or even your generator.
Access to Your Batteries
The considerate manufacturer has these coach and chassis batteries stored on a pull-out shelf for ease of service, usually near the engine and generator, if for no other reason than to minimize the length of the high-current wires required.
Typical RV Battery Voltage
I have to get at least a little technical on you. Here is some good information on what battery voltages should be in fully charged and partly charged batteries.
Your typical 12-volt battery, when fully charged, and with no load, should read 12.6 volts DC (VDC).
When you start your vehicle, the alternator will charge the battery, as controlled by its regulator circuit, starting at 13.2 to 14.4 VDC, depending on the amount of current the battery draws. It will drop to 12.6 VDC when fully charged.
The following table shows what the open-circuit voltage (with no load applied) will be under different static conditions, and the approximate estimated percentage of charge remaining on the battery:
Voltage and Charge Levels for RV and Auto Batteries
Notes About Charging
1. After fully charging, wait at least 12 hours to check the actual open-load voltage. This will allow the plates of the battery to stabilize and will provide a more accurate reading.
2. Almost all RV’s today, like automobiles, utilize numerous computers in their electrical systems, and it is not recommended to utilize fast-charge jumper chargers or booster packs to start an RV or car quickly, as the higher voltages can damage the computers.
If your batteries are maintained and used properly, you should never need a jump; but if you do, it is recommended to utilize a slow charger to avoid damage to the batteries and the RV electronics.
Coleman 10W Solar Battery Trickle Charger
I added one of these to my older Winny a few years ago, and it was great, as it kept my batteries charged when I had my RV in storage.
Good to Know: Electrical Battery Selector Switches
Again, I am staying away from describing all of the different electrical systems and accessories in RV’s and campers today. But, I do want you to know some simple facts about switches.
Manufacturers found out years ago that they had to include a selector switch (and often breakers or fuses) in battery wiring systems, for safety if nothing else.
It was quickly obvious to them that the potential current flow that had to be turned off and on was so high (under some conditions) that it was safer to use a low-current switch to control a higher current solenoid (or relay).
This is now pretty much the standard with all RV's.
Your RV will have a cabin on/off switch for turning off the 12-volt power to most of the cabin items that use this voltage. Whenever you leave the RV for a day or two, you should turn this switch off. This will reduce the drain on your coach batteries while you are away.
The coach switch location varies by vehicle design, but is usually near the coach entrance for owner convenience. Often the switch has an Indicator light of some kind on them to indicate that they are on.
Also your RV or camper will have a pair of master breaker switches that engage and disengage the two sets of batteries from the chassis and coach electrical systems. These switches are supposed to be used during long-term storage to reduce the current draw on your batteries. Also, they provide additional safety when you are maintaining your batteries.
RV Battery Disconnect Switch
To keep my RV battery charged, I had an electrician add one of these switches to my RV wiring and it worked great for me.
RV Battery Maintenance Tips
Questions & Answers
I have purchased a 78 Kingshighway, and it has electrical problems galore as far as I can tell. Is there a way to make sure that all the wires that are connected to the batteries are on the proper polarity? There is a major discharge in the system, and many battery wires were disconnected when I got it
First of all, there should typically only be one or two wires on the negative battery terminals. One will go to Chassis Ground, and the other (if it exists) would often go to a sensing circuit in your RV.
All of the other wires should connect to the Positive terminals of the battery.
As to your discharge problem, it looks like the previous owner had a problem himself, so it's hard to say what your problem may be.
One of the wires on the positive terminal is to the RV's Converter (Charger) which keeps the COACH batteries charged. So, make sure this is operating properly before you go chasing your discharge problem.
Then, I would check that EVERY accessory and appliance that runs on 12-VDC is working properly before moving on.
© 2010 Don Bobbitt