Not so long ago the precursors who have purchased and installed lithium batteries for off-grid applications could only rely on the manufacturers’ specifications to guide them. These batteries were designed for the Electric Vehicle market where speed of charge and ability to deliver high currents are most important. Over time, after extensive testing and many dead battery banks they have learned from their mistakes…
Learn about the optimal conditions and a few simple precautions to keep your lithium battery healthy for a long life.
Charge and discharge parameters given by battery manufacturers may not be the most appropriate
for the long term health of your off-grid lithium battery
They all agree that the manufacturers’ specifications are not applicable to the off-grid usage where battery performance over a long period of time (10-15 years) is expected. Although those precursors use batteries from different manufacturers, they all converge to the same conclusions. Here is a summary of the optimal parameters they have reached.
|Maximum charge voltage (bulk / absorption)||3.45 volt/cell (13.8 volt for a 12V battery)|
|Maximum charge current||< 0.3 C (120 A for a 400 Ah battery)|
|End of charge current||0.03 C (12 A for a 400 Ah battery)|
|Maximum discharge current||< 0.3 C (120 A for a 400 Ah battery)|
|Minimum voltage when to stop discharge||3.00 volt/cell (12 volts for a 12 V battery)|
|State of charge range (SOC)||10 % to 90 %|
|Ambient temperature||15°C to 25°C|
Other precautions to take:
- Stop charging when the battery is full (if that is not practical set the “Float” voltage to 3.3 volts per cell or 13.2 volt for a 12V battery)
- Do not keep the battery fully charged for a long time (when the battery is not used or in storage charge it to 50-60 % SOC)
- When the battery is not used for a long period, charge it to 50 – 60 % SOC and either:
- if you do not need energy: disconnect it from all systems – including battery monitor and BMS, or
- if you need energy: keep a solar panel connected and use a BMS that can control the charge to keep the SOC between 40 % and 60 % SOC (like the TAO BMS)
Be wary of equipment specifications
A number of charger manufacturers have based their charge parameters on the specifications from battery manufacturers. This may not be the best for your battery!
Our recommendation is to purchase chargers where the charge parameters can be adjusted (TAO BMS can also be used to compensate for chargers that cannot be adjusted).
Never trust the “Lithium” option on a battery charger
Check the parameters that are hidden behind that appellation
and compare them to the optimal parameters listed above