Originally Posted by DocMP
I emailed Peter at SMB about this and his reply was, "You can go ahead and store it just be prepared for the house battery to be drained when you take it out. In which case you can plug it in after to recharge it."
Wow, that is pretty much the most uninformed advice I have ever seen.
We have probably all seen the Cycle versus Lifespan Chart. And most try to adhere to the 50% rule, but the fact is that there are other important things that also affect the lifespan of our batteries.
Temperature, unless we all live in a perfect temperature of 77°F (25°C), temperature will have an impact on the life of our batteries. While higher temperatures result in higher capacity, this comes at a price to lifespan. For every 15°F increase in battery temperature the lifespan is cut in half. At 122°F the capacity is increased by 12%. Fortunately, or unfortunately the opposite can be said of low temperature. At freezing battery capacity can be reduced by 20%. At -22°F the capacity is reduced by 50%, the lifespan however has increased by 60%. Hopefully for most of us this will average out.
The other area where temperature comes into play, is charging setpoints. Our Absorption and Float values are also listed at 77°F (25°C), those will increase or decrease with temperature. The general value use is 0.030 (0.005 per cell) volts per °C. So, for every degree over 25°C the voltage setpoint will be reduced by 0.030 volts. Of course, the inverse is also true, for every degree below 25°C the voltage setpoint will be increased by 0.030 volts. This is where having a charger that can compensate for battery temperature comes in. Every decent battery charger can add a temperature probe, so that it can compensate to the correct voltage. This also includes your solar charger if you rely heavily on it
The time between discharge and full charge is another crucial input. In the normal process of discharging a battery lead sulfate forms, the sulfate is converted to lead and lead oxide during the charge process. Unfortunately, some of it never reconverts and is left behind. The deeper the discharge and longer time between recharging increases the amount left behind. Performing an equalization charge can get back some of the lost capacity caused by sulfation, unfortunately most AGM batteries don’t even have a procedure for this, and if they do it generally more complicated than flooded lead acid equivalent batteries.
This brings us to our next problem, and probably the number one item in decreasing the lifespan of our batteries, Partial State of Charge. If leaving our batteries in a discharged state for longer periods of time before fully charging is bad, the only thing worse is to provide some charge but not a full charge. That sounds reasonable, but who really treats our batteries like that. Unfortunately, the answer is most of us. If you rely on your alternator to charge your battery to full capacity, you are never getting there. Remember the absorption phase, we increase the voltage and gradually bring down the current to force the last amount of current into the battery. A normally regulated alternator just can’t do that.
The second misnomer is Solar, oh my solar controller brings it to a full charge. In many cases this is true, but it is very easy to get behind the curve. The thing that worries me when people talk about solar is that I am charged back up by noon. Did your charge controller go through a full cycle of absorption and then into float? But it is up around 13 something volts it must have, well not necessarily. Another misconception is I used 60 Amp hours since last charge. My two panels put out 10 amps of power, so I need six hours of good sunlight to charge back up. Never mind that you need to put more back in than you took out, that absorption phase gets us again. Once you hit the absorption phase, you begin gradually decreasing charge rate, so that 10-amp value doesn’t work. Many times, we will run out of sunlight before we complete the absorption phase.
Of course, we want to use are vans as intended, there is no way that we can guarantee to charge it back up every day. I generally shoot for at least a full charge once a week, if I’m out camping. The key will be to come home and put your rig on a good plug in charger and go through a full charge cycle. After that maybe solar will be able to keep you charge up, or you can disconnect the battery. A lot depends on how much current is being used while it sits in your driveway or garage. I like to leave my refrigerator on, in the winter this draw can be minimal, while in the summer it can be a big impact.
Unfortunately, all things never work as people design it. One of the problems of the float stage is when things come on and off. There are some reports of chargers being tricked into thinking they are not in float, and start the absorption phase again. This creates a classic over charging situation, so it is good to monitor your charger to see what the impacts are of current surges like the refrigerator or other low current devices coming on and off are. I probably monitor my rig more than most, I have never seen this happened on my rig. Another possible area of confusion is the solar charger, care must be made that they can work together. If unsure it is better to just leave the solar off.
My solar charger is more accurate than my Magnum Inverter/Charger, thus when my inverter/charger was in float mode, the solar charger would see it below the float mode set point that it monitored. After a set time from below float it would kick into absorption. Every morning it would come up end up going into an absorption phase. Luckily for me both chargers had programmable settings and I was able to find a spot where both are happy. If that wasn’t the case, turning off the solar charger would have been the easy solution.
With all that you may want to know what the easiest way to know, if the battery is full or 100% SOC. I recommend Balmar SG200 to keep track of your battery. You can read about it here http://www.sportsmobileforum.com/for...mar-22688.html