Battery on Shore Power

Is there a reason to keep it plugged in for those 3-weeks other than to keep the battery charged? If not, I guess I'd turn everything off, throw the breakers and not plug it in until 2-3 days before a trip.

The hills is where the Zombies come from. I wouldn't flee there.

AustinRoamers said:

I've read a lot of the posts on options for battery preservation.  We are able to keep our T@B plugged into shore power when not in use.  We plan to take her out about every 3 weeks.  Is there a reason we shouldn't be plugged in when idle?

Since you will experience some parasitic drain when not in use (e.g., via the USB ports, electronics, etc.) unless you have a means of isolating the battery you will want to as a bare bones minimum at least remove the battery fuse or install a battery on/off switch to eliminate any drain on the battery.  Even when unhooked the battery will discharge some when sitting idle as this is a normal phenomenon.  

If you are worried about it, plug it in for a few days at a time each week or isolate the battery after charging it up fully and charge it up once or twice a month in 2-3 day intervals to replenish the battery to a full charge level.  If you don't already have one buy an LED cigarette style plug in volt meter, monitor your voltage and maintain at least a 50% or greater charge level and you should be fine.

Dontcha just love all those little lights!    

Here is a chart I found here in the forums that is very different than Michigan Mike posted above. Look how a reading of 12.1 appears in each chart. So, which is more accurate???

My Max S is supposed to arrive around the 1st of March. Had the factory add a bracket for mounting dual batteries. Will see once it is here whether I end up with dual 24's, 27's, or a single 29 or 31. The dealer normally includes one size 24, so will need to work that out with the service dept. at my dealer and see what fits. In any case knowing I can go down to at least the 12.2 range on rare occasions and not feel to bad sounds good!

I would think hooking up a "battery tender" would be better than hooking it up to shore power all the time.  These are cheap and work pretty well.

My understanding is that most deep cycle batteries are designed for repeated DOD (depth of discharge) to 50%, 12.23 20 hour rating. I can't account for  

However, it is not as simple as this.  There is a trade off on repeated depth of discharge and life of the battery.  As long as it is not significantly drained (repeatedly to under 30% remaining capacity), the real tradeoff if generally played out in the life of the battery.  The horizontal scale is the depth of discharge.  If you repeatedly discharge to 50%, the battery would be good for 1000 charging cycles.  For my battery, dropping to 60% discharge repeatedly would lower battery cycle life to 800 cycles.  

There is thus a tradeoff.... you can draw 60% on a continuous basis (the 11.96% in Michigan Mike's diagram) and it will shorten the life in comparison to the same battery held to 50% DOD (12.1V).

These are the actual numbers from my battery charging procedures document prepared by Lifeline (my battery manufacturer).  They cite numbers comparable to Michigan Mike's chart.  

The only difference is that the lifeline (and several other citations indicate that deep cycle batteries should not be consistently discharged to below 50%.  Going to 60% DOD could reduce your battery life.  Since the estimate showing on the voltmeter is a relative (the actual measure desired is state of charge), the drop to 11.9 is generally a conservative estimate (the measurement is really only valid if the battery has been at rest (no in or out current) for a four hour period.

Bottom line, anything at or over 11.96 should not significantly affect your battery life.  According to my battery chart, the 10.5v lower limit is the total discharge place, not the alternative chart.  the detailed information for my battery matches Michigan Mike's.  You will note that Michigan Mike's chart indicates that at below 12.1, you are in orange area (not green). The last 10% does drop the life of the battery.  It still works, just the estimated battery life is shortened by 10-15%.  

The other table was done by Nick.  I would note that he was indicating these charges for T105 mounted in series, and trojan's literature actually indicates that the numbers in Michigan Mike's tables are the same for them.  Nick was attempting to measure SOC on his system, thou it appears that there were flaws in his equipment or logic, because he was indicating that the SOC at 12.1 was at 80% Depth of Draw, clearly not backed by the Trojan literature.  I suspect he was trying to map over some voltage measurements made with his trimetric meter to a measured SOC (from his trimetric meter).


Cycle life

Battery Cycles at various battery DOD battery

mash2, thanks for the thorough explanation! So, based on your info, I will try to keep it above 12.1, whenever possible. I assume most of our trips will be a mixture of with and without hookups and rarely over 3-4 days with no hookups, so I should be fine. Again, I really do appreciate the info. BTW: I have already gotten my Battery Tender so that when I get home I will plug into shore power for a day or so to insure I am fully charged and then switch to the Battery Tender!

mash2 - Didn't take it that way. - Always amazes me the analysis/detail ya'll get into though :-)

I definetly don't dance around on the pin head :-)