UPS batteries for pure solar application

moonbow

Hi, I have come across some C&D Technologies 12V 159AH UPS batteries (sealed Gel) for sale. The owner says they were used in a back-up battery system in a Govenment building but were never actually needed and not put under load. They were continually charged and poised for action but never were called to duty. The price is reasonable. Are these a good choice for my off-grid solar system at my mountain cabin? Thanks in advance.

Marc Kurth

Important points to be aware of when making a decision:

All types of lead acid batteries will sulfate when held at a full charge and not exercised. (It's sort of a "use it or lose it" thing) You would need to perform a capacity test to determine the status. You generally cannot equalize gel cells to remove sulphation.

AGM and Gel batteries do not suddenly die - they warn you by gradually showing signs of capacity degradation under load. Generally, we see UPS battery banks replaced when the storage capacity drops to about 70%-80% of the original.

Batteries designed for UPS duty are designed to be discharged heavily and quickly, but only occasionally. I do not have the numbers in front of me, but CD's UPS batteries generally have a short cycle life with constant charge-discharge cycles and less than perfect environmental conditions that are typical in off-grid applications.

So, there may be some life left in them, but everything depends upon your expectations and your view of the cost-to-benefit ratio.

moonbow

Thank you for that information. Based on the age of these batteries and the potential sulfation, I will most likely avoid them. The effort to acquire them, transport them and install them outweighs the discounted cost, especially when I am dealing with unknown factors like remaining storage capacity. Again, I appreciate your response.

706jim

Used batteries can be notorious for high voltage and zero capacity. I would buy new batteries.