Battery draining question

[jj5406]

I'm pretty new to RVing. We have been inveterate tent campers, but last fall purchased a used '07 (or '05 - somewhere around there) hybrid travel trailer (Jayco JayFeather 19-H) so I'm pretty new to many issues. Also, we typically look for more out-of-the way campgrounds and sites within campgrounds, so we are not likely to have an electrical hookup available.

We took the camper on a several day shakedown trip last fall and the only issue we had was that the battery drained down unexpectedly rapidly - resulting in a middle-of-the-night screeching alarm when the voltage to the lp detector got too low. This was unexpected because we had been very frugal with our energy usage to begin with. I recharged the battery by plugging back in to the towing hookup and letting our vehicle run for about an hour - probably got it up over 12 volts, but again it didn't even last a day. I can't remember if we had the fridge on, but we literally used nothing else after that except the occasional pump.

It could have been something unexpectedly drawing current, or just a bad battery (no idea how old the battery was - though it looked fairly new), so I figured I would just work out the details this summer.

This year I got a new battery (NAPA Premium Marine/RV Deep Cycle) with RC rating of 130. On our big camping trip this summer, everything seemed to be working fine. I had the fridge on and again we used minimal water pumping and even more minimal lighting (we have lots of LED lanterns). I didn't measure the voltage every day, but the idiot lights (good/fair/poor) indicated that the the battery was doing fine. One morning after about 6 days, we noticed that our fridge had turned off during the night. Propane was fine, but it was clear that the battery was too low (pump, and lights weren't working, but thankfully the LP alarm hadn't gone off). Battery idiot light now indicated poor. Checked voltage on the battery and it was at 8V.

I'm not sure how much juice the fridge draws just to be running on propane, but I figured that a week was probably a fair amount of time for a good battery to power minimal loads without needing to be recharged. So, I plugged in ran our vehicle again for an hour or two and charged the battery up to over 12V, which I figured should easily last us for the remaining 3 or 4 days we were planning to be there. After less than 24 hours though, the battery had dropped back to about 8V. There is one switch that is an override for all the cabin lights, and I noticed that it had been left on - so even though we were not using any lights, I thought there might be a phantom load that might be drawing juice. After that, I made sure that switch was off and I also pulled all the fuses except for the ones governing the fridge and the water pump (those two fuses also covers a few other auxiliary things). I charged the battery up to about 12V again, but by the next day it was again down to about 9V.

I'm no expert on batteries, but my limited understanding is that charging is non-linear; The first 80% or so is easy to charge and as the battery gets close to full, it gets harder and harder. Thus, when charging an electric car for example, you can get up to 80% relatively quickly, but getting all the way to 100% takes a lot longer. However, I thought that (assuming the battery is OK) the loss in voltage during use should be roughly linear under a constant load.

Unfortunately, I don't currently have a DC ammeter (though I think I will get one) to measure the current draw and isolate the problem (if there is one).

Does this sound normal? Am I mistaken about how the battery is supposed to work? Do I always need to charge it back to full when recharging? I'm not worried about shortening battery life by not always recharging to 100%, but I thought it should still work fine if not fully charged (especially on the very first recharge).

Once I get my DC ammeter, I can probably find out if there is an unexpected draw, and exactly how much the fridge draws. However, maybe a battery expert out there can tell me if this is actually the expected behavior and if so, why.

Thanks.

-J

[Harvey51]

my frig on propane only uses 0.30 Ah which to me is not much.
Of course you mean amp hours per hour or just amps. Sorry to be picky but we are trying to help someone understand how this all works.

Our fridge draws 0.4 amps all the time - about 10 amp hrs per day. That alone takes one 80 amp-hr 12 volt battery down to the dreaded half full level in 4 days. Note that if using 6 volt batteries, it takes 10 amp hrs out of each battery because they are in series and the same current goes through both - so you need twice the amp hr rating on 6 volt batteries to provide the same energy. I think misunderstanding this fact is the source of the belief that 6 volt batteries have greater energy capacity than 12 volt ones. The misunderstanding is in the units on this, too. The amp hour is a unit of charge, equal to 3600 Coulombs. Energy is measured in watt-hours or volt-amp-hours so you must multiply your battery's amp hour rating by its voltage to get the energy capacity. A 12 v, 80 amp hr battery has the same 960 watt hour energy capacity as a 6 V, 160 amp hr battery.

We share your desire to boondock without a generator. We just did 5 days on two batteries with a two hour drive in the middle that restored about 20 amp hrs according to my little battery monitor. I worked hard on the connections to get engine charging to work that well, just half a volt lost between engine battery and house battery when the engine is running. I will soon have 100 watts of solar charging to extend our boondocking time. Battery monitor thread

[Dakota98]

I STAND CORRECTED,

I SHOULD HAVE USED THE WORD "CONVERTOR" I SINCE HAVE EDITED THE ABOVE INFORMATION.

[beemerphile1]

Dakota98 wrote:
jj5406,

First of all, as I understand it. A "TRUE" deep cycle battery would be a 6-volt Golf cart battery. Put two into series & create a 12-volt system. The advantage is more long term power & stands up to discharge & recharge better than others.
Another key point in charging your batteries is by using the Inverter connected to either Shore power or a Generator, neither work very well, DEPENDING UPON YOUR INVERTER CAPABILITIES. Get the make & model number of your inverter & call customer support asking about its charging capabilities, if you don't find this information in the owners manual. Chances are you'll find out it doesn't put enough amps into a discharged battery to bring it back to a usable or full charge. Connecting to your tow vehicle via the plug, is the same thing. These connections are fine if the battery is already fully charged, you're noting using much power, if any, & you're simply wanting to "top it off"
If you want a better dry camping experience, get a small generator, a good "smart" battery charger & a "volt" meter connected directly to the battery. The meter will tell you the real voltage coming from the battery at any given time. A good voltage reading equates to good amperage, no need for an amp meter. Or go Solar ( $$$$$$ )
My inverter battery charging system according to the manual at best puts out 12 amps, but "factory customer support" told me 5-6 amps is reality.

PS: The coach battery monitor is absolutely useless.

Dakota98, I highly doubt you have an inverter charger nor does the OP. You most likely have a converter.

Although many of us do use 6v golf car batteries there are also 12v deep cycle batteries.

[Dakota98]

jj5406,

First of all, as I understand it. A "TRUE" deep cycle battery would be a 6-volt Golf cart battery. Put two into series & create a 12-volt system. The advantage is more long term power & stands up to discharge & recharge better than others.
Another key point in charging your battery connected to either Shore power or a Generator, neither work very well, DEPENDING UPON YOUR CONVERTOR CAPABILITIES. Get the make & model number of your convertor & call customer support asking about its charging capabilities, if you don't find this information in the owners manual. Chances are you'll find out it doesn't put enough amps into a discharged battery to bring it back to a usable or full charge. Connecting to your tow vehicle via the plug, is the same thing. These connections are fine if the battery is already fully charged, you're not using much power, if any, & you're simply wanting to "top it off"
If you want a better dry camping experience, get a small generator, a good "smart" battery charger & a "volt" meter connected directly to the battery. The meter will tell you the real voltage coming from the battery at any given time. A good voltage reading equates to good amperage, no need for an amp meter. Or go Solar ( $$$$$$ )
My Convertor battery charging system according to the manual at best puts out 12 amps, but "factory customer support" told me 5-6 amps is reality.

PS: The coach battery monitor is absolutely useless.

[westend]

12 Volt side of life

Battery University

Things noted: You got 6 days of use out of a single battery, that is about typical. You have an "idiot light" battery monitor, it is built for that type of user, don't rely on it. Charging from the umbilical connector when a battery is below 12V, is a losing proposition, it's better to use jumper cables directly from the truck to the trailer battery. Depleting a battery below 12V is reducing the capacity of the battery. Discharging the battery to 8V is damaging the battery, sometimes to the point of no recovery. Almost all batteries sold at retail with the label "Marine" are not a purpose built deep cycle battery. For RV use, Reserve Capacity is meaningless, we use the 20 hr. discharge rate which is measured in Amp Hours. 50% of amp hour rate is the golden threshold of usage, do not exceed it.

The number one thing you can do and is easy, is to replace the incandescent lights with LED bulbs. If you're going to be primarily boondocking, a battery monitor is a good thing to have. A hand held multimeter is a must-have and inexpensive.

Good luck with your 12V system.

[korbe]

BTW, my frig on propane only uses 0.30 Ah which to me is not much.

[beemerphile1]

jj5406 wrote:
...following information in the owner"s manual:

When pushing the “BATT” switch, the highest LED light illuminated indicates the estimated auxiliary battery condition. C = charge at 12.7 volts, G = good at 12.1 volts, F = fair at 11.6 volts, L = low at 6.0 volts....

Whoever wrote that part of the manual is absolutely incorrect and their keyboard should be confiscated. The other part of the manual has much more accurate info.

A deep cycle battery can be regularly discharged to 50% with no ill effects. It can be safely discharged to 30% but drastically shortens the battery life. In comparison a starting battery should never be discharged lower than 80%.

Many of us have two batteries, four batteries, or even more wired together to increase the available amperage.

[jj5406]

Well, thanks for the quick replies. Clearly I have a lot to learn about RVs and batteries - especially the useful voltages.

There is one thing that is still bothering me though and that is the conflicting information I have seen about deep cycle batteries. First off, there is a monitor panel in my camper with a battery charge indicator that has the following information in the owner"s manual:

When pushing the “BATT” switch, the highest LED light illuminated indicates the estimated auxiliary battery condition. C = charge at 12.7 volts, G = good at 12.1 volts, F = fair at 11.6 volts, L = low at 6.0 volts.

Yet in the same manual it also says: "A fully charged auxiliary battery will read 12.7 volts DC and 1.265 specific gravity at 80°F (32°C). The auxiliary battery is considered discharged at 11.8 volts, and dead at 11.65 volts. When voltage drops below those levels, permanent damage may occur."

How can 11.6 volts be considered "fair" and 11.65 volts be considered "dead"?

As for permanent damage, I've also seen both dire warnings about running your battery below 50% (12v) as well as other reports that it is not a big deal - just try not to do it all the time.

I had a choice of two batteries at NAPA. One was a "dual purpose" (DP) battery, but I got the one that was supposedly the true "deep cycle" (DC) battery. Apparently the DP battery is a cross, giving both deep cycle capability and cold cranking capability (but neither as good as a battery designed specifically for either of those two purposes).

I guess I don't understand the point of a "deep cycle" battery if it can't be *deeply* cycled. On the battery itself, it says "engineered to withstand the rigors of long, deep discharges and long slow recharges". I doubt I will be getting a generator to recharge the battery on a regular basis while camping, as we go camping to get away from that kind of noise. The real benefit of the camper for us is the comfort it offers us over a tent as we get older and especially the nice big dry space for us and the kids on all those bad-weather days in the AdiRAINdacks. Also, not having to leave the tent to use the bathroom in the middle of the night is really nice. But boy, I really love having that fridge.

I guess the best solution for us would be to just have a second battery on hand for longer trips. I am a little disappointed that the fridge draws (so much) battery power. The other propane fridges I've had experience with (two in no-electricity cabins, one in a circa 1980 camper) do not require any DC power source at all. It would be nice to have the option be able to run the fridge in a mode that uses no battery power - but retrofitting would be much more hassle than just having an extra battery on hand. Oh well.

At least I have learned that battery voltage drop is NOT linear and that the real usable voltage is only above about 11.6. I will get that DC ammeter and see if I can't measure the current draw of those things that are always on: the fridge (if in use) and the lp sensor.

BTW: I do have a nice solar panel, but unfortunately our fav camping spots are pretty shady. While not on trips (and not in winter storage), the camper lives down in our meadow. No electricity down there either, but lots of sun, so the solar panel should be able to keep the battery topped off.

Thanks again all.

-J

[Peg_Leg]

Plugging the 7 pin trailer plug into the truck is not going to get much juice to the battery. A set of jumper cables directly to the battery will work much better.

Some fridge's have a heater element to keep condensation from forming on the outside of the door. Some even have a switch to disable this little current sucker.

I have a LCD volt meter that I bought on ebay for $5 including shipping. Someone on the forum found one with a amp meter function.

[wa8yxm]

Some information: First Marine/Deep cycle batteries are starting batteries (marine) First and only lip service to deep cycle... GOLF CAR batteries are DEEP CYCLE from the drawing board to the delivery and install.

Page 2:

your 130 amp hours gives you around 50 usable amp hours.. A pair of six volt golf car batteries will more than double that (230 amp hours and you can use half or 115 before serious damage sets in).

They also recover from OH-@@@@ discharges better, though you should still avoid those.


Finally it takes several hours to properly charge batteries... The proper max charge rate for MOST batteries (LIfeline AGM is an exception) is 30 percent, so for a pair of GC-2 Golf car (230 amp hours) that would be 69 (Call it 70) amps.

At this rate if you take the battery to half full (130 amp hours) it will take about 2 hours to bring it back up to 90 percent, and 2-4 more to finish the charge using a 70 amp 3-stage converter (not your tow vehicle)

NOTE: You get nearly the same performance if you double up on what you have battery wise... Due to the differences between Marine/Deep cycle and true Deep/cycle the numbers come out nearly identical Just the lowest state of charge is higher.

[Matt_Colie]

Well J,

I'm glad you got 6 days out of the new battery, but as you pulled it down to 8 volts, you probably never will again. Discharging any Lead/Acid battery below about 12V can start a permanent capacity loss.

You have a lot to learn about living on batteries. Idling the TV main engine is almost a lost cause. The vehicle alternator will not be at full output. L/A batteries take time to recharge and there is just no way around that. When depleted as far as you did, it will literally take a day - or more to get back to 100%. It is best to start recovery long before that.

The only hope for your situation is to have some other means to charge the house bank. At your current level, solar could do a lot, but you would still do well to either plan to run the TV for hours or get a little genset. It has been my (painful) experience that the sun has a habit of being AWOL when you most need him.

Your choice is pretty much that or give up the lights, pumps and reefer. And don't try to run anything else either.

Matt

[korbe]

Our situation is similar to yours, in that we prefer batteries while camping (and no noisy generators). First thing I did was to figure out the amp draw of all my goodies. Then while conserving, tested my volts at the battery each day. We have 220 AH of power, and with not wanting the batteries to dip below 50% charge, we used about 8% every 24-hours (20 AH). So our 2 Trojan T105 batteries are drained down to about 50% after 6 days. And we have found that after 6 days, it's also time to refill the fresh water and dump the holding tanks. Sometimes we will plan a full hookup for a day to stock up and re-charge for another 6 days of dry campin.

[the_bear_II]

I find that with conservative use of 12v power a single battery will last about 4-5 days with 4 people. I carry a 1000w generator to recharge the battery daily. I run the generator for a few hours each day and it allows us to have 12v power without conserving for as long as we have fuel for the generator.

[beemerphile1]

Yes, normal.

Charging a severely discharged battery from the seven way connector could take 24 hours or more.

You charged it up to 12v???????? That is less than 50% charge.