RV off season battery maintinence, or not

Shadowcatcher · November 2013

I am seeing a question on the T&TTT (Teardrop & Tiny Travel Trailer) forum for some one winterizing their trailer and what to do concerning their deep cycle battery. I see this on other RV forums as well. Obviously if you have any parasitic loads i.e. radio presets smoke/CO detectors that pull small loads that must be made up. Even on my small trailer there is some drain from among others the Victron battery monitor and Morningstar RM1 meter everything else is disconnected by the main battery switch including radio preset and smoke/CO alarm.

I know that batteries self discharge at between 1% and 15% apart from loads and that AGM batteries less than wet cell. Potentially where I live temperatures can reach -20 F and a discharged or partially discharged battery is more vulnerable to freezing.
The range of options I see out there are.

Keep the RV plugged in to shore power with the converter maintaining the charge level at 100%. The progressive Dynamics converter goes through a 15 min boost ever 23 hrs or so.
There are battery maintainers that trickle charge a stored battery with varying levels of sophistication.
A small (10W to 25W) solar panel connected directly to the battery (unregulated) used on a number of trailer/motor homes.
Larger solar with solar controller that once it reaches 100% SOC...

Because of the danger of freezing I periodically (every couple of weeks) hook up the 185W solar panel to the Morningstar solar controller and let it run through a 24hr cycle which brings the SOC to 100%, (I have a LifeLine AGM).
I can get it up to 100% and pull the negative terminal from the battery (I am replacing the battery disconnect switch so that is the current state) and let it sit for four or five months, but what do I tell those that have the other options looking for advice?

waynefromnscanada · November 2013

Re: RV off season battery maintinence, or not

We hook up a 2.5 watt "battery Maintainer panel directly to the battery and leave it there all winter. Does not overcharge the battery and replaces self discharge. Works great on batteries from small rider mower batteries to large boat batteries that would / have otherwise gone dangerously low over Winter. We've been doing that for years in these parts. Example:
http://answers.canadiantire.ca/answers/9045/product/0112007P/no-coleman-2-5w-solar-battery-maintainer-questions-answers/questions.htm
Of course in our snow belt, we mount them vertically in Winter so the snow stays off, and of course facing South.

niel · November 2013

Re: RV off season battery maintinence, or not

generally a pv outputting at least 1%-2% of the ah capacity rating is good to use. always use some type of regulation on agm batteries so a cc is in order. you would be taking a chance of over voltage on your agm if you went without a cc as wayne suggested. you could get away with higher voltages on fla type batteries, but it would be a good idea to put a blocking diode for no cc circumstances to prevent discharge back into the pvs. (unless you wish to melt some snow)

waynefromnscanada · November 2013

Re: RV off season battery maintinence, or not

niel wrote: »

it would be a good idea to put a blocking diode for no cc circumstances to prevent discharge back into the pvs.

The unit in the link I provided has built in blocking diode, just attach the spring clips and forget it - - unless you have an AGM battery. This unit won't actually charge the battery, it's not big enough, so there's no danger of overcharging a flooded battery. It will however make up for battery self discharge so the battery will be good to go come Spring. It won't supply enough for parasitic loads, so unless you want to go with a bigger PV and a controller, disconnect all loads from the battery over the off season and just leave the maintainer connected.

Surfpath · November 2013

Re: RV off season battery maintinence, or not

waynefromnscanada wrote: »

The unit in the link I provided has built in blocking diode, just attach the spring clips and forget it - - unless you have an AGM battery. This unit won't actually charge the battery, it's not big enough, so there's no danger of overcharging a flooded battery.

Wayne, I would agree that a solar charger is the way to go (especially one with a small charge controller like the Morningstar Sun saver), with water level check every couple of weeks.

My first deep cell battery (a 12v 200 amp hr Trojan battery) was murdered because I used a plug-in battery tender like this. After 3 weeks the plates were exposed, and an already aging battery was shot..dead.

My layman's guess, but I think solar panel battery tenders are better for long term battery tending.
SP

PNjunction · November 2013

Re: RV off season battery maintinence, or not

As for what to recommend to others that may or may not be battery-savvy, for AGM users, as long as there is no parasitic drain, then just take advantage of the low self discharge and top them off every 90 days. More often say once a month if they store in high heat locations. Of course this assumes that they actually do store them after a full charge to begin with.

As for maintainers, my first suggestion would be to avoid the typical auto-parts smart chargers, which may actually do more harm than good if the user does not really know what they are doing, or know what their manufacturer warantee voltages are. I consider the major market for those are for trying to revive badly abused or neglected batteries. Some are good, some are bad, and many don't contain sufficient documentation about voltages and set points to stay within warantee specs of the battery.

If they want to get serious with a maintainer, then Battery-Minder is my top choice - the easiest to use would be the 2012 / 2012-AGM series. Why? Models are designed with very specific absorb and float voltages to meet your battery manufacturer's warantee. They also use continual temperature-compensation. In addition, while they promote "desulfation", the technique they use is NOT high-voltage pulses, but most likely some other waveform. Many here don't believe in desulfation, but since it does not use high-voltages, one can merely ignore this "feature".

Being a high-quality build is also refreshing to see. In addition to a 20 hour absorb timeout (if they bank was too large, or not charged up to begin with), they also test for bad cells or overall bad battery condition every 12 hours with a 10 minute test during float. Oh, and if one gets really serious about temp comp, they can get the optional on-the-battery temp monitor cable instead of the default ambient. You won't find these features in other tender manufacturers stuff. I have played with them all, believe me.

As an example of what to choose, the 2012 model has an absorb at 14.4 and a float at 13.4 volts. This is intended for FLA batteries, but also fits perfectly with your Lifeline AGM specs. The 2012-AGM model uses 14.7v absorb, and 13.6v float, and is more suitable to Optima and Odyssey batteries. If the others don't know what their battery specs are, perhaps you can help them out.

As for existing solar, I'd definitely put a suitable controller on them like those from Morningsar or elsewhere. If they have jumpers, tell them to go by the actual VOLTAGE ratings, and not necessarily the silk-screen. Ie, Morningstar's version of "sealed" is 14.1 volts, which is suitable for gel. But for FLA OR AGM, then pull the default jumper.

niel · November 2013

Re: RV off season battery maintinence, or not

as pnjunction said you could just leave them be and recharge them when you get back if not too terribly long of a time period. a maintenance charge certainly wouldn't hurt though. it is worthy to note that the batteries must have a full charge before leaving.

for the pwm sunsavers it is not necessary to put them at 14.4v when one is only doing maintenance charges as 14.1v is fine to use as the 14.4v is more for absorb charging, but being low current this 14.4v would not hurt anything either imo. if higher currents are available beyond about the 3% rate then stay away from the full absorb voltage.

PNjunction · November 2013

Re: RV off season battery maintinence, or not

Oops - correction - the timeout for the 2012 series is 20 hours in bulk, and 4 hours in absorb. If the voltages aren't reached in that time, or the absorb current does not fall below the cutoff limit, typically 100 - 500 milliamps, then the output shuts off and a diagnostic led is lit so that you don't fry a large bank forever with overvoltage, albeit with little current.

Niel is right about the small pwm Morningstars. The smallest, the Sunguard 4.5A version (14.1v absorb) would be the easiest no-brainer. And unlike a lot of cheap controllers, the Morningstars have ambient temp compensation. And pwm is far superior to the old-school on/off controllers that ping pong between an upper and lower voltage that typically come with the cheaper kits and rely on battery-hysteresis for regulation. Leave those ping-pong controllers back in the 1970's where they belong.

If one is a stickler for warantee voltages, like Odyssey batteries are, it pays to know exactly what voltages are being used by the charger / controller. It is one reason that Odyssey will not recommend Battery-Tender's (different brand from Battery-Minder !) that use 13.2-13.4v float. They are adamant about meeting 13.5v float.

techntrek · November 2013

Re: RV off season battery maintinence, or not

As I mentioned in another thread, I run a camper forum and this is another frequent question this time of year. For starters you should have a cutoff installed (a switch or a fuse) and always use it between trips. This keeps those parasitic loads from killing the battery. The LPG detector will kill it by itself within 2 weeks.

Then, once a month reconnect the battery and then plug in your camper to your house overnight. One night every 30 days, and also the night before a trip, and you'll be good.

Over the winter keep the battery on the tongue where it will stay cold. The life is extended 60% at -22 F according to the battery FAQ from Wind Sun. This also slows the self discharge rate so you can get away with only charging it overnight every 2-3 months while it is cold.

If - only if - your camper has a good 3 stage charger you might be able to get away with keeping it plugged in all the time, but you should check the water level often until you are sure it isn't boiling away. Another downside is it uses a ton of energy. My camper uses 31 watts "at rest" or 22 kw per month. Thats a trickle charge, the LPG detector, and the fridge brains.

Shadowcatcher · November 2013

Re: RV off season battery maintinence, or not

A supplementary question, There is periodically a discussion here of cycling, letting the battery get down to 50%, probably not a good thing in sub zero temps.
Folks use all sorts of methods, or none at all to take care of their batteries, with expensive consiquences.

PNjunction · November 2013

Re: RV off season battery maintinence, or not

Actual cycling down to 50% DOD once in awhile is a good thing as long as one charges it back up fully. Just make sure that RV group knows the difference between doing this, and just letting a battery self-discharge to that level. Big difference.

If they use AGM's, the simplest would be to top it off every month in hot weather, or they can go longer in cold climes. But to avoid freezing, the emphasis is on storing it with a full charge in the first place. If they care about the battery, they will look in on it once in awhile.

The battery-savvy already know what to do, however in many instances I've seen 5-dollar cheap tricklers attached to expensive batteries in $250K rigs. That's a false-economy for sure. If they want to do it right, there are options, although they may want to spend more than 5 bucks.

Shadowcatcher · November 2013

Re: RV off season battery maintinence, or not

Battery-savvy is a fairly rare beast among many/most RV'ers. I can't even guess how often when some one is talking about having an electrical problem that I have said "A VOM/multimeter is your friend, "you start with where you have power and go to where you don't and the problem is some place in between".
I suppose I need to come up with some sort of recommendation as to a range of trickle chargers that will do as little harm as possible.

PNjunction · November 2013

Re: RV off season battery maintinence, or not

Well, they should at least take as much interest in their battery as they do with the type of fuel and octane they use.

All they have to do is know if they are using Gel, Flooded, or AGM. Then, the manufacturer's spec for absorb and float voltage.

The reason I'm enthralled with Battery-Minder is that unlike some other "tricklers", they actually publish the owner's manual along with full voltage specs and descriptions and charts of the charge algorithm used. The desulfation feature can be considered benign for those that don't like it and can pretend it's not there. The 2012 models come with very specific voltages for gel, flooded, and even agm's that like 14.7v absorbs. Plus, there are NO buttons on the 2012's, so it is basically a connect and forget setup. That, along with continual temperature compensation at least makes it easy to recommend with a good conscience.

Not so with auto-parts store chargers. They can easily ruin a bank in a day if the op doesn't qualify the charger specs on his own. Other tender brands may provide very good docs, but forget to publish the specific voltages. While they might make a good charger, one could end up on the wrong side of the battery warrantee if it was examined by the bat manufacturer, and the finger pointing starts.

I'm really trying to avoid sounding like a shill for Battery Minder - but once I got one, I knew the difference immediately.

waynefromnscanada · November 2013

Re: RV off season battery maintinence, or not

Shadowcatcher wrote: »

Battery-savvy is a fairly rare beast among many/most RV'ers.

Haha "Battery-savvy" is an extremely rare thing among any portion of the population of the world. Battery? Is that the black box thingie beside where I dump in the windshield washer fluid?

Blackcherry04 · November 2013

Re: RV off season battery maintinence, or not

Since this thread is titled "RV off season battery maintenance" it might be nice that to point out that there is a big difference on using something on One Battery and a bank of two or more Batteries. These little dink battery minders can do more damage than they prevent on more than one battery. Most are two stage and once out of their Float range require they have reach a certain voltage before they return to float and they will keep on cranking their maximum capacity forever if they cannot reach that voltage.

I get this on Boats all the time where the owner has several batteries paralleled and they use a small charger over the winter and it will sit there and crank out 14.XX all winter long. They are like it had a green light when I left it, at some point the voltage dropped and they cannot get back to float.

RV off season battery maintinence, or not

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