Battery use

[swenny]

I just got back from a week of dry camping in the Black Hills of South Dakota. Beautiful weather and a great time. Most of the crowds are gone.

Question:

My trailer battery was getting weak and had a hard time keeping up with the fantastic fan running all night. Battery discharged to lower than 11.0 volts. the fan will keep on spinning to the last drop of battery power. I have a battery monitor to view voltage level. Everyday I recharge with Honda generator back up to 12.6

I started keeping my Caravan plugged in to the Scamp overnight to increase the battery capacity so that the fan would run full power all night. In the morning the battery monitor would read 12.5 volts so not much discharge (both still plugged in).

So...............am I damaging the caravan battery doing this? Everyday we drive a few hours sight seeing so the battery gets fully recharged (no trailer).

Any thoughts? Seems like a way to increase usable battery capacity.

Thanks,

Swenny

[thrifty bill]

Get the battery tested and replace it. RV batteries typically don’t last that long and yours sounds like it is done. I used mine for three days dry camping: all lights, fan for furnace and fantastic fan. Still had good voltage. Realize with LED lights campers don’t draw nearly as much nowadays. I assume frig was running on propane. If you were running frig on 12V battery will run down fast!

I never leave trailer plugged into TV when camping. You are risking being stranded.

[Darwin Maring]

Check the water level in the battery and fill with distilled water if low.
you can purchase a hydrometer at an auto parts store to check individual cells to see if you have a bad one. charge it up first B 4 checking.

[Glenn Baglo]

Originally Posted by Darwin Maring

Check the water level in the battery and fill with distilled water if low.
you can purchase a hydrometer at an auto parts store to check individual cells to see if you have a bad one. charge it up first B 4 checking.

Check first to ensure that the plates are covered with water, but don't top it up more than that. Then charge. Then top up the water.

[gordon2]

The above sounds like good advice, but the question was:

Originally Posted by swenny

...
So...............am I damaging the caravan battery doing this? ...
Any thoughts? Seems like a way to increase usable battery capacity.
...

So the question is not what to do about the trailer battery, but instead, is it a bad idea to leave the tug connected (and use the tug battery to run the trailer vent fan).

Bill hit on one issue, not being able to start the tug.

[stevebaz]

How old is the trailer battery? What % of the battery life is sitting unused and how are you maintaining the battery when it is unused.

In my case my trailer battery sits going unused over 90% of its life but during that time my battery is on a special charger that maintains the battery with different charge cycles to protect the battery and keep it charged. when camping we are plugged in or on solar to keep up the battery charge. My cheap walmart battery is over 5 years old now and still working well for us. But to be fair we are not heavy power users when we are camping.

[Glenn Baglo]

Originally Posted by gordon2

The above sounds like good advice, but the question was:

.

Sorry for offering good advice on battery use and maintenance. <_<

[Raspy]

Tim,

You are not hurting the tug battery by discharging it to 12.5 volts. But deeper and repeated discharges will hurt it as it's a starting battery, not a deep cycle battery.

And, as mentioned, if you pull it down too far, it won't start the tug. I've had that happen.

You may need a new deep cycle house battery.

When charging your house battery you should bring it up to 14.1-14.4 volts. Then ideally hold it there until the amps it can receive get down to about 5. This may be hard to measure, so make sure you bring it to 14.1 minimum and hold it there for a short time, in order to get to full charge. After resting for an hour or two, it should settle to 12.65 or so. This is fully charged. If you only charge the battery when it is fully discharged it won't last long and it will be hard to get it to full charge by just topping it off. While charging, 12.6 is not fully charged, that is a rested voltage.

[Franswa]

your story opens up several possibilities....


you may have a battery that does not accept a full charge anymore...


when you say you recharge to 12.6....when and how did you get the reading?....to fully recharge a deep cycle battery it has to get/see a voltage above 14V for a certain amount of time....


you may already know that running a battery down to 11V will shorten its usable life by a certain amount...


rule of thumb:
12.65+.....100% charged
12.4.....80%....if you can keep the battery from dropping below that level you will maximize the number of cycles that battery will yield before it dies of old age
12.2....50%...the level at which you should stop using power because you are now damaging the battery by continuing to draw power from it


all measurements made "at rest"....no load for a number of minutes (my batt. bank may be at 12.5V.... when I turn on a high demand item it'll drop to 12.2 sometimes....turn it off, voltage recovers to its new "at rest" voltage) I have a 4 digit panel meter that supplies a lot of useful info at a glance (in the pic below, trailer unplugged, 70W of solar on the roof, charge controller is "maintaining" the battery bank at 13.30, fully charged, the 16.6 is voltage from panels...if I cut the panels off that voltage (VOC) would probably go up to 20 or so....and the system voltage of 13.30 would start dropping VERY slowly)



notice that there is a lot of "certain amount", a "number of minutes" in this post...all vague terms....that's because there are not many absolutes in the battery biz.... exact measurements are hard to come by, if at all...it's half art, half science...good luck

[Steve L.]

Plugging into the tow vehicle battery overnight wouldn't work for me but then I have a factory tow package that isolates the two batteries when the key is off. You may have some sort of aftermarket tow package that allows the trailer to drain the tow battery.

I wonder how long you ran the Honda. As mentioned earlier the 12.6vDC number doesn't really mean much. My Fantastic Fan uses a little under 2 amps per hour (1.9) on low. That would be around 16 amp hours over night. Assuming you plug the trailer into the genny so that the trailer's power center recharges the trailer battery you'll probably have to run the genny 3-4 hours a day to get back to full charge. The charging circuit of the converter doesn't put a constant current back into the battery. It tapers off as it approaches recharged so recharge times can be much lengthier than one would first think.

I personally wouldn't recommend using the DC output on the generator. YMMV.

Articles I've read state that partial recharges are bad for lead acid batteries.

[John in Santa Cruz]

Originally Posted by Raspy

When charging your house battery you should bring it up to 14.1-14.4 volts. Then ideally hold it there until the amps it can receive get down to about 5. This may be hard to measure, so make sure you bring it to 14.1 minimum and hold it there for a short time, in order to get to full charge. ....

the power converter / charge controller should do this automatically, but it does depend on how new and what sort of power converter you have.

modern 3-4 stage ones will go through a bulk phase of up to 13.8V until the current drops to near zero, then go to an absorption phase of 14.2-14.4V for an hour or two until the current again drops to near zero, then revert to a maintenance stage with about 13.6V. To get a full charge on the battery, you want the generator running til you see the voltage go up to 14.x V then bakc to 13.x V.

older 'dumb' chargers just do the bulk phase of 13.8V or so and hold it there indefinitely.

you definitely need to leave the battery with NO charge power, and no significant load for a few hours before you can accurately read its charge state, where 12.6ish is 100% at 68F ambient temp (voltages vary by temp).

[swenny]

Thanks for the reply. I know my battery probably needs replacing (4 years old). I only plugged it in to the Caravan when I needed to get through my dry camping. After 6 hours of driving the battery showed a full resting charge of 12.6. After a couple days of dry camping it seemed to not have much capacity.
I ran the honda gen approx 1 hour in the morning and 1 hour early evening. The voltage indicator showed about 14 volts during charge and 12.6 after resting a bit. Probably not enough charge time. So will replace my battery soon.

Now...............about the use of the tug battery. It worked great for what I needed when I needed it. It didn't discharge much only down to 12.5. I monitored the voltage so I wouldn't be surprised by a dead battery not starting the vehicle. Probably not a good thing to do this all time as a starting battery is not designed to handle deep discharge. I consider it a shallow discharge.

It got me through and let me enjoy dry camping in the Black Hills.
The tug battery seems to be performing as normal.