Battery Basics for Your RV

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May 27, 2011

By Ken Freund

Batteries are essential for unplugged camping, yet they often get no attention until there’s a problem, which is often too late to save them. Here’s a quick primer:

Popular RV batteries come in three basic types: Conventional flooded electrolyte, gelled electrolyte and absorbed glass mat (AGM).

Flooded batteries have been around the longest, are most often supplied as original equipment and offer good capacity at moderate cost.

Gel batteries use a jellied electrolyte between the plates instead of a liquid, which costs more but won’t spill if tipped over, and they don’t require periodic refilling with water.

AGM batteries are more expensive but are maintenance-free, as the electrolyte is absorbed in matting wrapped around the internal lead plates.

RV batteries come in either six- or 12-volt ratings. Each cell has a nominal two volts, grouped together to form 6 or 12 volts. Six-volt batteries must be installed in pairs and wired in series so their combined voltage will be 12. Six-volt golf-cart batteries generally provide the most energy storage per dollar.

If used in pairs, 12-volt batteries must be wired in parallel (+ to + and – to -) so that their voltage remains at 12. When 12-volt batteries are used in pairs and wired in parallel, the stronger one will discharge into the weaker one.

RV deep-cycle batteries can be discharged and recharged more often and to a “deeper” level than lighter duty engine-starting batteries, which won’t hold up well if used as deep-cycles.

Battery life depends greatly on proper care and charging:

• Discharges of more than 50% of capacity shorten battery life.

• Don’t leave a battery at a low state of charge; recharge as soon as possible.

• Make sure charging voltage is within specifications.

• Many power converters will damage batteries if they’re left on for long periods, such as during storage. Use a “smart’ automatic voltage-regulated converter.

• Batteries discharge over time, and RVs have parasitic current draws. Disconnect the batteries and use a special maintenance-type charger during storage (not a converter or trickle charger).

• Batteries with removable caps need periodic checking and refilling with distilled water.

• In hot weather and when frequently cycled or overcharged, batteries will use more water.

• If the electrolyte level drops below the top of the internal plates, the battery may be damaged.

• Clean corrosion from terminals.


Ampere-hour (A-H) capacity is calculated by multiplying the current in amperes that the battery can deliver by the time in hours of discharge until voltage drops to 1.75 volts per cell (10.5 volts for a 12-volt battery).

Reserve Capacity (RC) is the time in minutes that a fully charged battery can be discharged at 25 amps until reaching 1.75 volts per cell.

Cold cranking amperes (CCA) equal the number of amperes a fully charged battery will deliver at 0°F for 30 seconds and maintain at least 7.2 volts (for a 12-volt battery). Cranking ratings are mainly important for engine-starting batteries.


• Wear rubber gloves and eye protection when working with batteries.

• Batteries produce hydrogen gas that can explode from sparks from loose terminals and improper jump starting.

• Connect the last jumper cable negative clamp to a clean metal ground on the chassis, rather than to the battery.

Leave a Reply


  1. Lee

    I have read it is better to change all the batteries at the same time and get them from the same batch and date that way you change them all out the same time. In this case I would just buy the one but check out Sams Club they have good prices. I have also seen batteries from Interstate with different warranties 30 m0nths check the part numbers on their batteries. I have talked to people about using 6v golf cart batteries and some say it works and some say it did not last. I think I will just stay with 12v duel dray cell / charging batteries. I only have room for 2 large batteries not 4 small and I dont think I would go to 2 smaller batteries for power.

  2. Lee

    I have a question, I have had my travel trailer for 5 years. Checked the batteries, have 2 12 volt both wired for the inverter feeding them, they are not tied in together at the batteries. Trailer was purchaced new from a dealer. I just recently checked the flood level and charge level. one battery has 75% of it’s power and the other has a litttle more like 85%. Thinking about purching new batteries soon and then a bout a week or two later the battery that was down to 75% blow up. Not sure why. It was real hard to see the level in the batteries. I did over fill one and took some out of it but brought them to the max level so I don’t think it was over serviced. Could the tester have weekend or shorted the battery when used. I used two different kind. One is electronic which they say does not hurt the battery, I don’t trust it and the other tester shorts the battery with a load. I am think the one with the load tester may have done something to the plates and caused a short. I have used thes testers on a lot of different batteries over the years and I never had a battery blow up. The trailer is pluged in to keep the batteries charged up all the time. It has never had any problems being pluged it.

    We had gone on a trip recently and found that the batteries did not last as long as the have in the past. Most of the time we are pluged in when traveling this is what lead to me checking the batteries and finding out the generator would not start to charge the batteries. It took 3 days to find jumper cables to start the generator and get them back up, then every thing was fine during the trip. I also purchaced solar panels to keep them charged during the day to keep the batteries up to start the generator if needed. I don’t want the same thing to happen again.

  3. John Echoff

    We purchased a used class A in August 2011, it had all batteries installed new in June (12v & 6v). one of the 6v totally discharged and drained the other three 6v’s. Now I find that two of the warranties on the Interstate batteries is valid for only 6 months, the Excide is good for only 12 months. Can anyone give me a lead on a battery with a decent warranty, don’t want to think of replacing 3 or 4 batteries per year.


  4. Steve

    I agree Greg. Same goes for level/ stabilizer jacks. Why are they rated 5000 to 7500 lbs but your told not to use them to level?

  5. Mike

    Even Wal-Mart carries the newer style smart trickle chargers. Very inexpensive.
    As for Gel Cells…they are marked as such. Pretty much all others are flooded electrolyte. (add water)
    You will recognize AGM batteries by the price tag!!

  6. greg

    I’m always disappointed with articles about batteries. The terminology doesn’t match the product. My battery label makes no reference to flooded electrolyte, gelled electrolyte or absorbed glass mat (AGM). I haven’t noticed deep cycle in the stores but suppose they exist. Mine says Marine cranking, which I guess is an engine starting battery. And the battery chargers I’ve seen in the stores don’t use terms like “special maintenance-type charger”. Haven’t seen the term trickle charger in years. And I wouldn’t even want to ask a clerk about “a smart’ automatic voltage-regulated converter”. (?)….

  7. Brian

    OK all you battery experts! Tell me if I’ve been given bad advice. When I purchased our travel trailer in 2006, the dealer told me to take the battery home between trips, hook it up to a small DC lamp bulb and let it drain the battery dead. When the light has finally gone out (two or three days, usually), hook the battery up to a trickle charger and bring it back up to fully charged. Continue this discharge/recharge cycle until the next trip, then, after the trip bring it home and do it all over again. “Batteries love exercise!”, was his mantra. I have now been doing this for five years with the original battery, always removing the caps and topping off with distilled water when necessary. I have had no problems with it, although our actual dry camping times have been very limited. Bad advice or not?

  8. Dana Moses

    I was going thru two 12 volt batteries in parallel every year. I now have two 6 volt golf cart batteries in series and have not had any trouble for three years now. I have a fifth wheel with a smart charger on the convertor.

  9. Thom

    When I am plugged in for a long time in a park, 2-4 months, how do I keep my battery from overcharging? Should I pull the fuse in the fuse link I have going to my positive pole? Will disconnecting my battery hurt the built in charger? Thanks!

  10. Richard Plude

    We have a 05 BT Crusier built by Gulf stream. 30 ft c camper. We have on slide out that has a low leak. We have taken it to 3 RV centers and it is now in the third one. There is no water trail on the walls so they are all saying it is a low leak and they have tried every thing and cannot fix it. Now we are thinking about putting on a apron as it has a sky light the reason there is no apron.
    The water gathers on the main camper floor below the slide out floor.
    wondering what your thoughts are on this.
    Than You and would appreciate your input.
    Richard Plude

  11. I respectfully disagree with the reply to Eric in that a battery should not be discharged below 12 VDC. By the definitions in the basic article, the absolute minimum battery discharge voltage is 10.5 VDC (Amp Hour capacity … until voltage drops to 1.75 volts per cell (10.5 volts for a 12-volt battery).) I have a digital voltmeter permanently attached to the terminals of my coach battery and have it mounted where I can readily monitor it. I stop discharging when the voltage just drops below 11.0 as this should be about the 90% discharge (10% charge state) point. From here the battery needs to be charged to at least the 80% charged state I don’t have any scientific data to support this, just about 40 years of messing with batteries and determining what seems to work best.

  12. rtpn60

    Always store batteries in a cool, dry, well ventilated place. Also use a float charger. Do not use a regular car charger as these often over charge your batteries. With a smart charger and proper care batteries last 3-5 years even here in AZ where it is very hot and hard on the batteries. Another thing that reduces battery life it discharging them too low. If it is truly a deep cycle lead acid do not discharge it below 12v as you will shorten it’s life. Using a regular car or truck battery as a deep cycle is also bad as they were not designed to be drained that far.

    The concrete floor is an old wife’s tale. It just that people left them there and they were neglected and went dead so it MUST have been the floor! hee hee hee

    Good reading here….

  13. eric

    Ugh, what was I thinking? We store it in our BASEMENT not our garage, as our garage is detached, unheated and well, let’s just say not the best place to store anything.

  14. eric

    Thank you for this information about batteries. During the course of our 3 years experience with RVing (we haul a 30 ft Conquest), batteries have been one of our sore spots. We’ve gone through more batteries in these 3 years, it’s ridiculous. I’ve lost count but I’m on either #4 or #5. I’m getting better, but they irk me. (One fell out of an open truck bed, and I’ve no clue what happened to it. I just pray that no one was hurt by our carelessness!)

    So, I DO have 1 question for you, Ken. When we are not on the road or in camp, I remove the battery from the trailer, and take it home. I store it in the garage, on a wooden shelf, a little way off the ground (I read somewhere to NEVER EVER store it on concrete). When needed I just hook er up and go, and let the current from the truck charge it while we drive. This includes after our 8 – 9 month winter.

    Should I be doing something else?