The Toaster Needs New Batteries: Time For Lithium?
About a month ago we realized our RV batteries were no longer performing at full capacity. Since we were plugged into grid-electricity while we were staying at Crystal Mountain Resort, we didn’t realize this about the batteries until one evening when the whole mountain lost power. While the rest of employee housing was pitch black, our batteries kicked in to power everything while we rocked out to music and made dinner. That only lasted a couple of hours before our inverter tripped on low voltage. But we knew from the past two years of experience that we should be able to go much longer. This meant something was up with our batteries.
What’s the problem with our batteries? Essentially, they’ve prematurely aged. This means that once they are fully charged, they don’t last as long as they used to. Let’s compare it to a cell phone. Once your phone gets to a certain age, its battery life decreases. Instead of being able to use it for 10 straight hours before having to charge it again, it can now only last for 5 hours. That’s the issue we’re experiencing with our RV batteries. The question is why? What happened to cause them to do this? Before I answer that, I need to provide some background information.
The Toaster’s Batteries
The Toaster has 8 Interstate GC2-XHD lead acid 6-volt batteries. If you know your batteries, you’re probably shaking your head saying, “Well that’s why your batteries are shot – they’re crappy batteries.” Yes, we fully acknowledge that these Interstates are not high quality batteries like Trojan or Surrette. In fact, that’s precisely why we got them.
Before we moved into the Toaster, we had absolutely no idea if living in an RV that’s 100% powered by solar panels was even going to work. This was essentially an experiment and we didn’t want to spend a lot of money on Trojan or Surrette batteries only to potentially ruin them. That would be wasting a lot of money. Instead, we figured we’d try living in an electric fifth-wheel using cheaper batteries. Thanks to Jerud’s work discount at the time, we spent $1,121 including taxes and 6 core charges for all 8 batteries. Going with the Interstate batteries saved us several hundreds of dollars than if we got nicer ones.
The Lifespan of a Lead Acid Battery
It’s difficult to measure the lifespan of a battery. That’s why battery manufacturers provide a cycle number where one cycle stands for a full discharge to 50% and a full recharge. The 50% discharge is at a given rate of discharge which is usually pretty low/slow (the rate of discharge is how fast you use your electricity/charge).
The thing with lead acid batteries is that the faster you discharge a battery, the less capacity you can get out of them. Discharging a battery faster is harder on it. Our Interstate batteries are rated to have 650 cycles. High quality batteries are rated for 1,200 – 1,500 cycles.
Did We Ruin The Toaster’s Batteries?
That’s the big question: did we ruin our batteries having them power an all-electric RV for the past two years?
Yes, we prematurely aged them. As I previously said, the Interstate batteries are rated for 650 cycles. This means we would have had to fully discharge them to 50% and fully recharge them back up to 100% every day for 650 days. We didn’t get 650 cycles out of them.
We know this because we rarely brought our batteries down to 50%. Most days we’d only bring them down to 80% and the next day they would recharge to 100%. Sometimes we wouldn’t be able to recharge them back up to 100% for a day or two. We also had days that we kept the batteries floating (at 100%) either because the Toaster was stored or we were staying with friends, or when we had a lot of sun and didn’t use a lot of electricity.
But, considering how hard we used them, we got pretty good life out of them.
What We Did Right & Wrong
What we did right with the batteries:
We never took them below 50%, ever.
We only took them below 60% 3 times.
We also equalized and watered them regularly.
What we did wrong with the batteries:
We used large amounts of energy rapidly. Lead acid batteries don’t like that.
Part of the problem is that the meter that tells us our batteries’ state of charge is designed to assume that people use their batteries at a relatively low rate. But we used our batteries at a higher rate. This means that when we thought the batteries were still 70% full, they were probably closer to 60% full. And when we thought they were 50% full, they were actually emptier.
So, while we thought we were treating our batteries well, we were actually discharging them too far.
How Could We Have Prevented This?
We could have prevented our lead acid batteries from prematurely dying by:
Purchasing higher quality batteries that have higher rated cycles from the start.
If we had realized in advanced that we use battery power at such a high rate, we would've designed the battery bank differently – as in have a larger battery bank. But we didn’t know any better at the time.
We could've used less of our current battery bank. This would've meant that instead of stretching them thin and staying on solar during several rainy days, we would've used solar and batteries for 2 days and then gone to an RV park to plug in until it was sunny again. This would've been gentler on our battery bank.
Lithium Batteries Is Our Solution
After we realized we need to replace our current batteries, Jerud and I talked a lot about what to replace them with. The three things mentioned above are all options, but there are issues with each:
Getting higher quality lead acid batteries would allow us to get more than 2 years out of them, but they would still prematurely die. It would still be a waste of money and materials.
We actually can’t build a bigger battery bank because we don’t have the physical space for it in the Toaster.
We could change how we use our batteries and plug into grid-electricity during long periods of rainy days. But we want to remain 100% solar powered.