Battery on Shore Power

AustinRoamers

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?

jkjenn

The factory has expressed concern that this could lead to a shorter converter life.

Nomad

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.

AustinRoamers

Only so we are ready to flee for the hills with a full charge when the zombie apocalypse happens.

ChanW

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

Nomad

:-)

Michigan_Mike

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.

Nomad

Be aware that the little monitor lights don't match the charts - as above. Their green light is 12.5 and above. At 12.4 it's goes orange.

Michigan_Mike

Dontcha just love all those little lights!    

AustinRoamers

Thanks all for the useful information.

jctangney

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???

Nomad

I think the other one as 12.5 on my meter and on my solar controller indicates full (100%). Also was talking to a van camper a couple of days ago and he goes to 11.9 all the time with no apparent harm to the batteries - his are now almost three years old and were cheapy Walmart offbrands.

jctangney

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!

Nomad

I'm a night owl so up till 1:00am at least - Usually sitting at 12.2 after having the lights and Alde on. Wake up at 12.2 - That seems to be the idle spot and my norm. I don't pay much attention and start shutting things off unless I see the meter go red at 11.9

EWizard

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.

charlieborton

Our 2016 T@B outback came with a battery disconnect switch just like the one shown above.

mash2

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

Nomad

Here's my simple calculation - When my battery no longer holds a charge, I'll get a new one. Sticking to my daily routine until then ;-)

jctangney

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

jctangney, my research generally indicated that 12.1 or up was uniformly fine... no magic, but I wouldn't sweat anything above 12.0.  I personally just try to keep it above 12.0 (I'm one of the solar group with lots of battery capacity so it has seldom been an issue for me).   

Pxlated.  Not trying to knock your routine.  One of my points was that running down to 40% won't cause the system to have problems, but that the impact may be on the length of battery life.  There is nothing magic about 12.1 or 11.9 that will cause anything catastrophic failure... just a potentially different life for the battery and only if your battery recommends avoiding DOD of 50%.  I was just reporting on the technical documentation that was reported in my battery charging guide.  Unless you use a sophisticated meter, I just consider the voltage a rough estimate of voltage anyway.

I must say I found it interesting that the alternative table was based on "sophisticated" monitoring by the user (Nick, author of the other table presented by jctangney) and presented some really strange conclusions regarding capacity (inconsistent with his battery manufacturer as well).   

Nomad

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

mash2

Don't mean to go crazy, just trying to frame the real issue.  There is nothing magical about 11.9 or 12.1, but all are certainly below the other chart that was offered -- which had a different purpose or was faulty (I read the article and it was really about translating readings to the SOC reported on his meter... something was amiss with one of the readings).  I would guess it was the SOC he was matching.  The estimates on my MPPT controller have always been a bit squirrely with a dual battery setup.

I actually agree with you.. get a routine that seems reasonable and stick to it.  I think that sometimes we all get lost in believing in artificial accuracy and then dance around on the head of the pin to justify it.  

I kind of like getting out the manual and seeing what they said to do (what a strange idea).

Nomad

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