Comparison of Lithium Batteries

The 3 most common type of lithium batteries according to battery university are

Lithium Cobalt Oxide(LiCoO2) — LCO

  • Most Common, ideal choice for mobile phone, laptops.
  •  Short Lifespan is not suitable for Solar Lights

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)

  • Ideal choice for power tools and electric vehicles

Lithium Iron Phosphate(LiFePO4)

  • Used to replace Lead Acid batteries
  • 2,000 + life cycles, and very safe
  • LiFePo4 is safer and has a longer cycle life

We did our research and have chosen LiFePO4 as the battery choice for our solar street light. It stands out of the crowd because it has the best safety and the longest life. Under the right conditions a life expectancy of 20 years.

Lithium Iron Phosphate(LiFePO4)
Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
Lithium Cobalt Oxide(LiCoO2) — LCO

Found in

Lithium Iron Phosphate(LiFePO4)

Solar Lights

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)

Electric Vehicles

Lithium Cobalt Oxide(LiCoO2) — LCO

Mobile Phones / Laptops

Cycle Life

Lithium Iron Phosphate(LiFePO4)

2,000 + cycles

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)

1,000 – 2,000

Lithium Cobalt Oxide(LiCoO2) — LCO

500–1,000 cycles

Saftey

Lithium Iron Phosphate(LiFePO4)

⭐⭐⭐⭐⭐
Thermal Runaway 270°C

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
⭐⭐⭐⭐ Thermal Runaway 210°C

Lithium Cobalt Oxide(LiCoO2) — LCO

⭐⭐⭐ Thermal Runaway 150°C

Power / Weght

Lithium Iron Phosphate(LiFePO4)

90–120Wh/kg

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
150–220Wh/kg

Lithium Cobalt Oxide(LiCoO2) — LCO

150–200Wh/kg

Lithium Iron Phosphate(LiFePO4)

AGM vs LiFePO4

AGM is an alternative battery for Solar Street Lights. AGM (Lead Acid) also known as the the car battery. 

I have summarised information from Sealed Performance.

  1. 100Ah 12.8v LiFePO4 has 60% more capacity vs 100Ah 12v AGM
  2. LiFePO4 has up to 4x faster charge rate vs AGM
  3. LiFePO4 has 6x longer life cycle vs AGM
  4. LiFePO4 has less then half the weight if AGM

The cost to replace an AGM battery should be a big consideration when choosing what type of battery to use.

If an AGM battery needs replacing every 3 to 5 years then it will end up costing more in the long run.

Lithium Iron Phosphate(LiFePO4)

AGM Deep Cycle

Weight

Lithium Iron Phosphate(LiFePO4)

12.2 Kg

AGM Deep Cycle

27.5 Kg

Cycle Life

Lithium Iron Phosphate(LiFePO4)

2,000 + cycles

AGM Deep Cycle

300 cycles

Charge Rate

Lithium Iron Phosphate(LiFePO4)

2 Hours

AGM Deep Cycle

8 Hours

Power / Weght

Lithium Iron Phosphate(LiFePO4)

90–120Wh/kg

AGM Deep Cycle

45Wh/kg

Depth of Discharge (DoD)

Lithium Iron Phosphate(LiFePO4)
90% (From our tests)

AGM Deep Cycle

50%

Not all LiFePo4 batteries are the same

Have you ever wondered why some batteries are more expensive than others?

It is because they are built with different quality control checks.

We get calls from customers who purchased a solar light from ebay or china that does not work anymore. When we test the light we find that the battery is faulty. The cause is a faulty cell from a cheap battery.

Most lithium batteries consist of many 18650 or 26650 cells.

For Example: A 30AH 12.8V battery will have 40 cells. A 60AH battery will have 80 cells. A Tesla S contains 7,104 cells.

If any of the cells are faulty, the whole battery becomes faulty. The bigger the battery, the more cells and slightly bigger chance of a faulty cell.

I can’t stress enough how important it is to have premium quality 18650 or 26650 cells.

 

What can you do to extend the life of a LiFePO4 battery?

  1. Buy from a reputable retailer. 
  2. Do not over charge the batteries. By doing this you stress the batteries and increase the chances of a cell becoming faulty.
  3. Do not over discharge the batteries. Flat batteries also create stress on the cells.
  4. Keep batteries at room temperature.

What are the ideal charging parameters

  • The most voltage of a LiFePO4 cells is 4.2V, we do not recommend you charge the battery to more than 3.6V
  • For less stress on the battery, charge it to 3.5V
  • There is less than 1% extra capacity between 3.5V and 4.2V.
  • By overcharging you increase the stress on the battery and reduce the lifespan.
3V

12V

24V

Maximum Voltage

3V

4.2V

12V

16.8V

24V

33.6V

Recommended Maximum Charge Voltage

3V

3.6V

12V

14.4V

24V

28.8V

Recommended Maximum Charge Voltage #2

3V

3.5V

12V

14.0V

24V

28V

What are the ideal discharging parameters

  • The BMS must disconnect when the battery at 2.5V. Mild damage can occur when the voltage is under 2V
  • Discharge to 2.8V to reduce stress on the battery
  • There is less than 5% extra capacity between 2.5V and 2.8V
3V

12V

24V

Ideal Discharge Voltage

3V

2.875V

12V

11.5V

24V

23V

Ideal Discharge Voltage #2

3V

2.8V

12V

11.2V

24V

22.4V

BMS Cutoff Voltage (Battery is Empty)

3V

2.5V

12V

10V

24V

20V

No. 15Ah 24V battery has a higher capacity than a 20Ah 12V battery.

To compare the capacity of batteries of different voltages we convert to Watt Hours (Wh)

The formula to convert is Amp Hours x Voltage = Watt Hours

  • 20Ah 12V has 240 Wh
  • 15Ah 24V battery has 360Wh

It is a good idea to multiply Amp Hours by the Voltage to get Watt Hours.

To avoid confusion batteries of all types should use the Watt Hours (Wh) method.

Visual Representation of Ah and Wh

3V

12V

24V

30 Ah (Amp Hours x Voltage = Watt Hours)

3V

96 Wh

12V

384 Wh

24V

768 Wh

768 Wh (Watt Hours / Voltage = Amp Hours)

3V

240 Ah

12V

60 Ah

24V

30 Ah

Discharge #1 - 12.8V 30Ah (384Wh) LiFePO4 @ 7.5A

  • 12.8V 30Ah is also 384Wh.
  • 95% of the battery capacity is within 11.5V – 13.5V.
  • It is not worth the risk to damage the battery by going beyond the recommended voltage range. The 5% gains is very small.

Discharge #2 - 25.6V 45Ah (1152Wh) LiFePO4 @ 5A

  • 25.6V 45Ah is also 1,152Wh.
  • 95% of the battery capacity is within 23V – 27V.
  • It is not worth the risk to damage the battery by going beyond the recommended voltage range. The 5% gains is very small.

Conclusion

The batteries that we use in our Solar Street Lights are excellent quality.

We test them with our West Mountain Radio battery analyser.

The battery returned with a rated capacity of 98.7%.

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