Inherited a 12v system - question about adding battery capacity

[dialingwand]

We acquired some land with a small off-grid array. I'm not sure what the panels are.

- Charge controller: Morningstar PS-30 (https://www.morningstarcorp.com/products/prostar/)
- Batteries: 2x Crown, Deep Cycle CR-235 (6v) in series (12v) (https://www.crownbattery.com/hubfs/Downloads/Deep-Cycle-Batteries.pdf)

We'd like to add two more batteries (2 parallel 12v series).

The question I have for the experts here: would new batteries degrade more quickly if the existing batteries were themselves very degraded? Should I test the existing batteries (try to get the current capacity?) before expanding the system? Or (last question I promise) would it be more wise to just get 4 new batteries and replace/expand the batteries all at once?

I don't know the state of the current batteries. They seem fine, and the system runs reliably, there just isn't enough battery capacity to power the small fridge overnight. The panels themselves are able to keep the two existing batteries charged and power the fridge (during the day) even on overcast days when there's never any direct sunlight.

 

[Q-Dog]

It is rarely a good idea to add new lead acid batteries to old lead acid batteries. That said, no one can make a decision without information. You need to know the state of the existing batteries ... and "they seem fine" isn't good enough.

 

[dialingwand]

That's fair. Thanks.

 

[mikefitz]

All new batteries would be ideal. Without knowing the panel watts it's difficult to confirm you have enough power to run the fridge and charge the batteries. The solar controller is PWM type, so it's possible to get more solar yield with a MPPT type controller. ( subject to the temperature in your location).
More details of fridge model/ working volts and current , and inverter if used would be helpful.
My guess from the available information, is ,a) you don't have enough solar, or b) the batteries have reached end of life

However replacing the batteries would be a useful step and further changes could be made if required.

 

[wme]

Basic lead acid batteries tools.. A volt meter and a hydrometer. Before you do much you need to really know what shape your batteries are in.

 

[dialingwand]

Tools on order to "understand the state" of things. Already had a multimeter. Hydrometer was less than $10. Appreciate the input and will report back here with results (and decision) in a little while.

A few things:
- Temps get really cold.
- Will poke at the fridge with a P3 Kill a Watt
- Leaning towards getting 4 new flooded lead acid batteries because the two currently installed likely been discharged below 80% regularly. Certainly below 50% regularly in their current state before we got the system.
- Our long term plan (2 years) is to replace the current system with a 48v system with server rack batteries, and all-in-one controller/inverter and new panels (the current panels are about 10-12 years old). But I have a lot to learn so the current system is a great "jump in and get comfy" while I form some experience and build some knowledge.

 

[50ShadesOfDirt]

I like the long-term planning ... very smart; consider adding:
- sidestep cold issues with insulated structures/boxes to hold critical gear; if you are handy, this is easy to do.
- AIO's are possibly iffy in terms of warranty/support ... plan on learning a lot, test-driving the one you choose, have spare(s)
- learn about LF vs HF inverters; some choosing to do

Thoroughly document the existing system (you'll learn even more):
- what loads are present, what will you (want) add in future
- solar panels are existing; find the spec/info label on the back, read off everything, and add it to the 12v documentation
- get manuals/docs for your inverter/charger/mppt unit, and read thoroughly to understand
- draw a diagram to see how the former owner tied everything together; find the fuses, panels, determine wiring sizes, etc.; they may have made choices you won't agree with, and a few fixes might keep the place from burning down.
- compare existing system diagram to this forum's resource on 12v ... is yours good enough to hold you until the 48v gets in place, or does it need to be dumped sooner vs later (do you need to go to 48v now)

More considerations:
- skip FLA and jump into LiFePO4 batteries now; 2 x 12v100ah will fit the current 12v system, although you'll need to verify if Morningstar component understands charging LiFePO4; no maintenance, tools, etc. if you dump FLA now.
- if you do implement 12v now (reuse or rework existing), it can move to a 12v hand-truck or camping system (be reused), so little to no loss there.

Hope this helps ...

 

[wme]

Tools on order to "understand the state" of things. Already had a multimeter. Hydrometer was less than $10. Appreciate the input and will report back here with results (and decision) in a little while.

A few things:
- Temps get really cold.

What is low temp in battery room?
FLA's do have a place in our world of solar.