batteries if not in use?

solarsquirral · January 2015

hi
i have a off grid cabin that i leave unattended anywhere from 2 weeks to 4 months
ive heard that a fully charged deep cycle will lose 15%charge per month so im guessing
4 months is the longest to leave it even after a full charge

is it better to take the battery off the controller and put it in storage (maybe insulated)if not used for 4 months
or leave it chargin multiple shallow charges

does a battery only have a certain number of cycle in its life???
better to store????

solarsquirral · January 2015

Re: batteries if not in use?

the batterys are 4 6v rolls surrite 550 420 ahr at 20 hr
wire in series parallel 12 volt sytem

should i remove all connections also wire etc

or just shut off at control panel

BB. · January 2015

Re: batteries if not in use?

For flooded cell deep cycle batteries--It is better to recharge them every 30 days... Letting them go longer can accelerate sulfation.

You would typically need around a minimum of 1%-2% rate of charge for a battery in good shape. Use a small PWM charge controller+panels, or just leave your solar system connected and charging (turn off AC inverters and all other unneeded loads that could kill the battery bank in bad weather or if something goes wrong with the charge controller).

Self discharge is a function of age and battery temperature... If you batteries are left to sub freezing weather (and are fully charged when you leave), they will self discharge slower. If they are over ~75F, they will need charging even more often (hot batteries age and self discharge faster).

-Bill

706jim · January 2015

Re: batteries if not in use?

solarsquirral wrote: »

hi
i have a off grid cabin that i leave unattended anywhere from 2 weeks to 4 months
ive heard that a fully charged deep cycle will lose 15%charge per month so im guessing
4 months is the longest to leave it even after a full charge

is it better to take the battery off the controller and put it in storage (maybe insulated)if not used for 4 months
or leave it chargin multiple shallow charges

does a battery only have a certain number of cycle in its life???
better to store????

My place sounds a lot like yours. My batteries sat unused for about 6 months every season and due to snow cover, were likely uncharged for 4 continuous months.

They lasted 19 seasons and finally gave up the ghost this year. (Purchased 1996).

I'd just leave the panels hooked up and all should be fine. Do turn off all loads however.

Mountain Don · January 2015

Re: batteries if not in use?

We leave our off grid cabin for a month or so at a time throughout the winter. We leave the PV and CC connected and working to maintain the battery charge. All loads are disconnected. In 5+ years we only had one problem. That was when we were struck by lightning and just about everything with a semi conductor in it was toasted if it was still plugged in. Even though the inverter was turned off. We now have considerably more lightning protection apparatus including air terminals and grounds as a general "diversion" system. During the summer lightning season we do now physically disconnect the wires from the PV to the CC when we leave. When we are there and lightning threatens we also disconnect the incoming from the PV. Ten foot separation.

So if you are in an area with frequent seasonal lightning take that risk into account. We don't worry about that over the winter as lightning is a very rare winter occurrence where we are. Battery self discharge is more of a worry. especially because if the snow is heavy it could be three months between visits.

solarsquirral · February 2015

Re: batteries if not in use?

hey thanks for the input

i check in on the cabin more often these days every week or so

would i be better off shutting off the controller and turning back on every two weeks for a full recharge

instead of chargeing everyday

i just want to make sure im not hurting my bank with these shallow cycles

Mountain Don · February 2015

Re: batteries if not in use?

If the system is just sitting there with nothing on that uses battery power the batteries are not really cycling. There would be a brief bulk charge first thing (to replace the self discharge), then the absorb for however long it is set to run , then float for the remainder of the day. If the absorb was overly long you could use up some water. In our case I have never had to add water during the winter season. After winter I don't usually need to add any water until maybe June. Even then there is still plenty of plate cover. YMMV.

icarus · February 2015

Re: batteries if not in use?

Mine sit for months at a time, fully connected to the PV. I have two panels that are wall mounted so they always get a bit of charge. They are always fully charged when I return. You should monitor the water useage carefully, and perhaps I might consider lowering the absorb time some, and perhaps the float voltage just a tiny bit to make sure they don't use too much water. A few ah of charge every day is not going to hurt.

My original set of t105s is going on 16 years and still seems to holding up fine, although they get very limited use. My main set is now six years old and act as new.

Comes nder the category or why mess with success, especially if youare there every couple of weeks to monitor the water.

Tony

batteries if not in use?

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