Now that we have talked about 12.8V, let’s deepen the understanding of lithium batteries. The nominal voltage of a single cell of lithium iron phosphate is 3.2V. When we use a 12V system, we connect four cells in series, so 12.8V is obtained. Many RV users are also very confused about the full voltage and the discharge voltage. This is very simple. The nominal value of a single battery cell is 3.2V. Generally, the maximum voltage of the built-in protection board is 3.65V, and the empty voltage can be up to 2.5V, but the basic setting is 2.8V. The conclusion is drawn: 4*3.65V = 14.6V when fully charged, and the voltage is 4*2.8V=11.2V when the battery is less than 10%.
Here a question that most concerned about are: If we feel that the battery in my RV is not enough, can I buy another set to increase the capacity? We see that many users are chaotic. For example, if they have a 400AH battery and a 600AH battery, the ideal state is to reach 1000AH, but this is not the case in actual use. When lithium batteries are connected in parallel, they will be based on the maximum capacity to calculate the cumulative value. Similar to the above parallel method, the number obtained should be 800AH, and this parallel method is not scientific and is prone to problems. So why is it so? Let’s explain. Assuming when you charge a 400AH battery, the single-cell voltage is 3.2V/400AH (multiple blocks in parallel) and a 600AH battery, the single-cell voltage is 3.2V/600AH (multiple blocks in parallel), you are charging two sets of batteries at the same time, and the capacity of the battery is related to the voltage. The built-in protection board also judges whether the battery is overvoltage. Under the same conditions, when the 400AH battery is charged to 3.65V, it starts the protection, feedbacks the battery voltage to the charger, and lets it stop charging. At this time, the 600AH battery is only charged to 400AH, it cannot reach 3.65V.
If you must use lifepo4 batteries for parallel connection, you must ask the manufacturer whether the built-in BMS can be connected in parallel? What is the maximum number of parallel connections that can be made? Similar to our BL-1280 the built-in BMS can support up to 4set parallel and series connection. In any case, please be sure to consult in detail before deciding.