Victron energy LiFePO4 Manuel page 4

2 General information about Lithium iron
phosphate batteries
Lithium iron phosphate (LiFePO4 or LFP) is the safest of the mainstream li-ion
battery types. The nominal voltage of a LFP cell is 3,2V (lead-acid: 2V/cell). A
12,8V LFP battery therefore consists of 4 cells connected in series; and a
25,6V battery consists of 8 cells connected in series.
2.1 Rugged
A lead-acid battery will fail prematurely due to sulfation if:
• it operates in deficit mode during long periods of time (i. e. if the
battery is rarely, or never at all, fully charged).
it is left partially charged or worse, fully discharged.
•
A LFP battery does not need to be fully charged. This is a major advantage of
LFP compared to lead-acid.
Other advantages are the wide operating temperature range, excellent cycling
performance, low internal resistance and high efficiency (see below).
LFP is therefore the chemistry of choice for very demanding applications.
2.2 Efficient
In several applications (especially off-grid solar and/or wind), energy efficiency
can be of crucial importance.
The round trip energy efficiency (discharge from 100% to 0% and back to
100% charged) of the average lead-acid battery is 80%.
The round trip energy efficiency of a LFP battery is 92%.
The charge process of lead-acid batteries becomes particularly inefficient
when the 80% state of charge has been reached, resulting in efficiencies of
50% or even less in solar systems where several days of reserve energy is
required (battery operating in 70% to 100% charged state).
In contrast, a LFP battery will still achieve 90% efficiency under shallow
discharge conditions.
2.3 Size and weight
Saves up to 70% in space
Saves up to 70% in weight
2.4 Endless flexibility
LFP batteries are easier to charge than lead-acid batteries. The charge
voltage may vary from 14V to 15V resp. 28V to 30V (as long as no cell is
subjected to more than 4,2V), and they do not need to be fully charged.
Therefore several batteries can be connected in parallel and no damage will
occur if some batteries are less charged than others.
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