I didn't know we were discussing lead acid batteries. With a 5 year warranty I just assumed they were LiFePO4 because most lead acid batteries don't come with such long warranties specifically because if they are kept at a low state of charge (like if 2 panels aren't connected) it drastically shortens their lifespan.
I looked up Northstar and they were specifically known for making AGM lead acid batteries. 3-6 years would be considered a good run for them with daily cycling.
Since we also don't know what the warranty says, with lead acid I'm going to guess that it's a pro-rated warranty, meaning that if they are 4.5 years into a 5 year warranty that means 6 months pro-rated out of a 60 month warranty equals a refund or credit of 10% the original price.
If that's the case, and I hate to be the bearer of bad news, potentially getting 10% back probably isn't worth the effort, especially if "potentially" is the operative word. Did the disconnected panels shorten the life of the batteries? Maybe probably. Can it be proven? Probably not. But at 4.5 years of daily cycling those batteries were probably at the end of their life regardless of the warranty.
Will they give the 10% back? They might do it as a customer service gesture, the scrap value of the lead in the batteries might be worth that much, so for them it could be a wash. If it's in the form of credit, you have to decide if you want to do business with them in the future.
Like others have said, it's recommended to only go with LiFePO4 moving forward. The price on them have dropped to the point where they are the only type of battery that makes sense to buy for a solar system. They look like they have a higher upfront cost, but you'll get twice the useable power out of them compared to similarly rated lead acid batteries and they will last 10-15 years instead of 3-6. They can also charge faster than AGM so you can potentially collect more power with fewer panels because they won't resist charging as there is no absorption phase. I was originally resistant to buy into the higher up-front cost of LiFePO4 until I did exhaustive research and realized I was a fool to wait as long as I did, and the prices are almost 50% lower now than they were then. Just for your awareness, your charge controllers will probably have to be reconfigured or reprogrammed to use the different chemistry.
I looked up Northstar and they were specifically known for making AGM lead acid batteries. 3-6 years would be considered a good run for them with daily cycling.
Since we also don't know what the warranty says, with lead acid I'm going to guess that it's a pro-rated warranty, meaning that if they are 4.5 years into a 5 year warranty that means 6 months pro-rated out of a 60 month warranty equals a refund or credit of 10% the original price.
If that's the case, and I hate to be the bearer of bad news, potentially getting 10% back probably isn't worth the effort, especially if "potentially" is the operative word. Did the disconnected panels shorten the life of the batteries? Maybe probably. Can it be proven? Probably not. But at 4.5 years of daily cycling those batteries were probably at the end of their life regardless of the warranty.
Will they give the 10% back? They might do it as a customer service gesture, the scrap value of the lead in the batteries might be worth that much, so for them it could be a wash. If it's in the form of credit, you have to decide if you want to do business with them in the future.
Like others have said, it's recommended to only go with LiFePO4 moving forward. The price on them have dropped to the point where they are the only type of battery that makes sense to buy for a solar system. They look like they have a higher upfront cost, but you'll get twice the useable power out of them compared to similarly rated lead acid batteries and they will last 10-15 years instead of 3-6. They can also charge faster than AGM so you can potentially collect more power with fewer panels because they won't resist charging as there is no absorption phase. I was originally resistant to buy into the higher up-front cost of LiFePO4 until I did exhaustive research and realized I was a fool to wait as long as I did, and the prices are almost 50% lower now than they were then. Just for your awareness, your charge controllers will probably have to be reconfigured or reprogrammed to use the different chemistry.