Author Topic: adding batteries to string?  (Read 299 times)


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adding batteries to string?
« on: August 11, 2017, 08:54:50 AM »
I know adding batteries to a string is not recommended. However....

I have  4 Deka gel batteries installed a year ago. Most of the time they have been continuously charged from my large PV system, as if they were connected to the grid. They have only been on the small  PV system for 20-30 days, and never discharged to 50%.

I want to add 4 more identical batteries. I know I have to be careful about cabling lengths.

Would doing this be stupid, or just a minor degradation in capacity/life?
Way off grid
Old system: Outback 2524, 1200 W PV,  installed 2005, 384 amp hours
New System: 2 SMA 6048 with 2 Midnite Solar Classic 150 controllers, 5500 W PV, 1700 amp hours


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Re: adding batteries to string?
« Reply #1 on: August 11, 2017, 12:59:01 PM »
I think the issue if more with the age of the batteries - their life cycle begins with when they are manufactured.
So over time as the first batteries age and might need tweaking to their voltage or ending amps setpoint, it would be more difficult to do with some one age and the other different.

So not recommended but that doesn't mean I wouldn't do it depending on if you are talking about series or parallel , the expectations for lifespan, the use, and monetary costs compared to replacing the whole pack.  There are a few considerations to think about. 

Ideal would be to try to find someone who would want to buy your 4 batteries for a halfway decent price and replace them all with new ones.

system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie