Lithium batteries or Lead-Acid batteries? While choosing a solar battery bank for your camper and boat can be a difficult task. If you just switched over from AGM to Lithium (LiFePO4) Batteries for your battery bank. I believe you had already made your choice.
he two most popular types of solar battery banks are Lead-Acid and Lithium. While gel batteries are also an option, we aren’t going to talk about them today because of their many flaws (need to be vented, keeping up with chemistry, water levels, etc.).
Lithium Batteries – Are They the Right Choice for You?
Well known as Lithium and LFP batteries, Lithium Iron Phosphate (LiFePO4) batteries deliver high energy and power density on mobile applications. LiFePO4 often have the best combination of performance, safety feature and reliability and environmentally friendly characteristics for motorhome and marine applications.
One of the significant benefits of Lithium Iron Phosphate batteries is the deep cycles and lifetime span when compared to the Lead-Acid batteries on the market. When choosing batteries bank for mobile applications. Weight is one of the biggest considerations. LiFePO4 batteries are roughly a quarter of the weight of the Lead-Acid batteries in equivalent useable capacity.
What are the differences between Lead-Acid and LiFePO4?
- A 12V lead-acid battery has 6 cells. There are no electronics inside the battery, therefore it is easy to accidently damage the battery through improper use.
- A lithium battery will (almost) always have a Battery Management System (BMS) in-built. This can be sophisticated and have features that protect the cells from short circuit, overload, measure and display the current, State of Charge (SoC) by Bluetooth and also balance the cells or be simple and only disconnect the load/charge when a cell voltage is low/high.
- The BMS on lithium batteries disconnects the load/charge by the use of MOSFETs, these MOSFETs are commonly the limit on the continuous current rating of the battery. If the battery is rated for 100A continuous, and you have a 2000VA load, then you will be drawing approximately 167A from the battery and you will destroy the MOSFETs almost immediately.
- Deep cycle lead-acid batteries are rated at their 20 hour rate, i.e. if you discharged a 100Ah battery at 5A it would be completely discharged in 20 hours. If you discharge it at 20A, you’ll be discharging it at the 5 hour rate and it’s useable capacity will be reduced by around 20%. Lithium batteries do not suffer from this problem, however depending on the internal resistance of the lithium cells, discharging at a high current towards empty may cause the BMS to disconnect the battery so allow 90% useable capacity.
- Most lead-acid batteries are rated for 600 cycles at 50% Depth of Discharge (DoD) whereas many lithium batteries at 2000 cycles at 100% DoD. This means the battery will be at 80% of its original capacity after that number of cycles, of course these figures are highly variable based on factors such as discharge/charge rates, temperature, vibration etc.
- Lead-acid batteries prefer to always be full, you should always leave these on a float charge if in storage if possible. Lithiums prefer to be stored at 40% SoC.
- You cannot use lead-acid PWM chargers with lithium batteries, the lifespan of the lithiums will be reduced as the lead-acid batteries require longer absorption periods (the point towards the end of the charging cycle that holds the voltage higher to ensure the battery gets full). Whereas lithium batteries have a very high charging efficiency and do not require these long absorption periods so the absorption voltage will cause voltage induced stresses within the cells negatively affecting their life. In fact, lithium batteries will last longest if used between 40-60% rather than 0-100%.
- 100Ah of lithium is rated at 12.8V and therefore 1280Wh compared to 100Ah of AGM which is rated at 12V and therefore 1200Wh. It makes more sense to speak in Wh or kWh than Ah, but Ah at 12/12.8V is the predominant term in the automotive industry.
The Cost of AGM vs EnerCore Lithium Batteries
In most people impression. The biggest drawback of a lithium battery bank for your solar setup is the upfront cost. 2x 200AH of LiFePO4 batteries will set you back $1,900 in the market. The Trojan AGM batteries with a bank of 4 batteries for a usable bank of 200AH costs about $1,152. So choosing AGM over Lithium will save you $748. That’s a pretty big savings, right?
Well, cost is not issue anymore here at Rolling Cart.
But comes to the long-term costs and replacement costs.
Lifespan of Lithium Batteries
EnerCore lithium batteries are designed to last 2,000 to 5,000 cycles. For this example, we are going to use the worst case scenario of 3,000 cycles. A ‘cycle’ is when a battery is drained, then recharged. Again, for the sake of the example, we will say a cycle is one day (use your batteries all night, then let them charge up during the day when the sun comes up). Denver gets an average of 300 days of sunshine per year, so in Denver, we would expect this battery bank to last 10 years at full capacity.
After that initial 7-8 years (2,000 cycles), the battery is still expected to hold 75% of its capacity, meaning that you would still have 150AH usable battery bank.
Lifespan of AGM Batteries
AGM batteries are designed to last 1,000 cycles. Considering AGM battery to be bad once it reaches 50% of it’s capacity. Comparing that to EnerCore 75% capacity isn’t exactly comparing apples to apples. The Lead-Acid batteries will reach 75% capacity at around 525 cycles.