One of the most readily available chemistries of Lithium batteries is the Lithium Iron Phosphate type (LiFePO4). This is because they have become recognized as the safest of the Lithium varieties and are very compact and light when compared to lead acid batteries of comparable capacity.

A common desire nowadays is to replace a lead acid battery with LiFePO4 in a system which already has a built-in charging system. An example of one is a sump pump battery backup system. Because the batteries for such an application may occupy much volume in a confined space, the tendency is to find a more compact battery bank.

Here is what to be aware of:

★12 V lead acid batteries are comprised of 6 cells. In order for them to charge properly these individual cells require 2.35 volts to charge completely. This makes the overall voltage requirement for the charger to be 2.35 x 6 = 14.1V

★12V LiFePO4 batteries have only 4 cells. In order to realize complete charge its individual cells require 3.65V volts to charge completely. This makes the charger overall voltage requirement 3.65 x 4 = 14.6V

It can be seen that a slightly higher voltage is required to fully charge the Lithium battery. Therefore, if one were to simply replace the lead acid battery with lithium, leaving all else as is, incomplete charging can be expected for the Lithium battery – somewhere between 70%-80% of full charge. For some applications this may adequate, especially if the replacement batteries have a much higher energy capacity than the original lead acid battery. The battery volume reduction would give major space-saving and operating at less than 80% maximum capacity would enhance the life of the battery.