Just before going full-time with our mobile life in 2012, we got our first solar powered system -- 80 watt panel, basic charge controller, and 1 lead acid, deep cycle, marine battery. It worked just fine and we soon learned how to live with the power we could collect each day. We experienced some battery issues when we didn’t store our first battery properly over a very cold winter, but took better care of our second battery and got over 4 years of power from it.
In 2018, we upgraded our panel to a Renogy 100w Solar Suitcase and noticed an immediate benefit in terms of charging time and low light efficiency. Just 2 months ago, we swapped out our trusty old battery for a Renogy 50 Amp Lithium Iron Phosphate battery. Interested in DIY? Check out our YouTube video to learn how to properly install a Lithium battery .
In this post, we will discuss the pros and cons of this battery upgrade, and what we have noticed in terms of battery efficiency, charge time, and output.
Size & Weight:
The new Lithium Iron Phosphate battery takes up about 1/2 the space (in terms of volume) and is about 1/3 the weight of our previous battery.
Our 12V (13.3 V when fully charged) 50Ah Li battery provides us with a maximum of 665Wh. We can use 100% of those Watt hours because it is Lithium. Previously we used a 12V 78Ah deep-cycle marine lead acid battery, which provided us with 936 Wh. As a lead acid battery is only effective to 50% capacity, we only had 468Wh available for use. Now, even with a smaller battery, we have an additional 197Wh.
While we never had any major problems with our lead acid battery, there is the potential for fire due to the build up of gases coming off the battery during an overcharge cycle or when improperly charging. Lithium Iron Phosphate batteries are more stable and far more difficult to cause overheating problems. Always using an appropriate charge controller to charge the battery minimizes this risk.
The extent to which you use your battery, and the temperature range to which it is exposed, will affect its longevity. Most deep cycle batteries will average between 3-5 years, with 3 years being far more the norm and a great loss of efficiency after that time. Lithium batteries are designed to last up to 10 years, with a slight loss of efficiency. While we’ve only had this product for 2 months, we cannot yet comment on its lifespan.
We’ve noticed that our new Lithium battery rarely drops below 70% capacity with average usage, and is often charged back up to 100% before we finish breakfast. Now, to be fair, it is spring and the sun is rising early. As we’ve traveled through Canada this spring, we’ve seen all types of weather, including 3 full days days without much sun. During this time, the battery never dropped below 70% with average usage. Even on a very overcast day, our 100w panel was able to bring the charge back up to 100%. Comparing this with our previous lead acid battery, 3 days of clouds and average usage of power would drain the battery completely.
We decided to test the battery one evening to find out what would drain it completely. We started with an 82% charge, turned on the inverter, and plugged in our LED lights and Shari’s high-power laptop (for photo and video processing) on a bright screen setting, and with an external speaker to watch a long movie. It drew the battery down to zero in about 1.5 hours. Comparing this with our previous lead acid battery, we would have only gotten about 20-30 minutes.
One small downside we’ve noticed is with running our 12V DC Fantastic Vent Fan all night. If we don’t start the evening with nearly 100% charge, the fan (even on the lowest setting) will drain the battery sometime before dawn. With our previous lead acid battery, the fan used to just slow down as the battery got lower, but it never fully quit. After speaking with a Renogy engineer, we learned that this issue is an inherent quality of the two types of batteries. With the lead acid battery, as the charge diminishes so does the voltage of the DC appliance, allowing it to run at a lower and lower speed for longer -- thus, prolonging the discharge. With the Lithium battery, the voltage remains constant until the battery charge is fully depleted, thus it runs the fan at the same speed until it doesn’t run at all. In the summertime, we need to make sure our battery is fully topped off each day if we want to run the fan at night
Our new 50Ah Li battery cost $500. Our previous lead acid battery cost about $120. Is it worth it? Let’s break it down to the price you will pay for each usable unit, by Watt hour over the number of cycles rated for each battery.
In the comparison below, you’ll notice that you will still pay less for 3 lead acid batteries (3 x $120) than 1 Lithium battery (1 x $500), but when you look at the cost per Watt hour per cycle, it’s a much different story.
For our previous lead acid battery (78 Ah, 85 cycles), we got an effective Wh of 468. (78 Ah x 12 V = 936 Wh; but, remember that lead acid only delivers effective voltage to 50% of its capacity, so the usable Wh is actually 468 Wh per cycle.)
1404Wh* / $360 = $3.90 per Wh (*using approximately 3 batteries over 9 years)
At $120 per battery , each Watt hour costs $3.90. Divide that by the number of cycles ($3.90 / 85 = $.046 Wh/cycle).
Forour new Renogy Lithium battery (50 Ah, 2000 cycles), we get an effective Wh of 600 (50 Ah x 12 V = 600 Wh). Lithium will deliver effective voltage until depleted so we can use all 600Wh.
600Wh* / $500 = $1.20 per Wh (*using just 1 battery over 9 years)
At $500 per battery , each Watt hour costs $1.20. Divide that by the number of cycles ($1.20 / 2000 = $.0006 Wh/cycle)
Thus, the cost per unit is significant. Lead acid = $.046 Wh/cycle and Lithium = $.0006 Wh/cycle. Wow, it’s a long term pay off, but you certainly get more bang for your buck!
After using this battery for a couple of months, we are impressed with its performance. We are getting more Wh out of a smaller battery, it is safer, tops off faster with minimal sunlight, will likely last 3 times longer, and is less expensive in terms of Wh/cycle in the long run. We’ll check back in at the end of the year to report on a longer term performance.