THE FRONT BOOT
HOW LITHIUM
BATTERIES
CHARGE
Lithium iron phosphate (LiFePO4) batteries have
very different characteristics and composition
to other batteries used for RVing. As such, they
require different battery chargers.
Like most battery types, LiFePO4 batteries have
individual cells that are rated at 3.2V each for a
total output of 12.8V. The problem is that once an
individual cell is charged, a traditional charger will
turn off the current. For this reason, any LiFePO4
battery should have its own inbuilt management
system to ensure that all cells are charged equally.
So what does the charging profile – the way
voltage and current vary during a full charge of
a battery – of a LiFePO4 battery look like? This
differs depending on the type of battery, from
lithium to AGM.
For example, a fully charged lead acid battery will
have a voltage of around 12.6-12.7V, whereas a
LiFePO4 battery has a voltage of around 13.3-
13.4V at full charge. At 20 per cent capacity, a
lead acid battery will have a voltage around 11.8V,
whereas a lithium battery will hold its voltage at
about 13V.
A LiFePO4 battery has a much smaller voltage
tolerance and, because of that, the ‘trickle’
charge of the deep-cycle battery does not apply.
This means a LiFePO4 battery can be charged
faster while minimising the risk of overcharging.
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A typical charging voltage for a 12V battery varies
between 12.9V and 14.1V. While a constant voltage
and current will charge a battery quickly, it’s better
for a deep-cycle battery’s health if a ‘trickle’ charge
is used over a longer period of time.
LiFePO4 batteries operate a little differently but
an appropriate charge is also best for maximum
battery life. Generally speaking, a constant current
will flow until the battery reaches 90-95 per cent of
its state of charge. Once that point is reached, the
current will reduce, while the voltage will do the
opposite, rising to a cut-off voltage of a theoretical
16.8V (but in reality is usually around 14.7V).
The bottom line is that not all chargers are
created equally – ensure your charger, or
the one you’re considering buying includes a
LiFePO4 charging profile.
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