RV FEATURE
DOLLAR
AND SENSE
IN PART 4 OF OUR SIX
PART SERIES ON LITHIUM
BATTERIES, WE LOOK AT
HOW THEY STACK UP ON
A COST BASIS.
If you’re the sort of caravanner who rarely
leaves the confines of the bitumen and
spends most of your time in a caravan park,
then save yourself reading further as lithium
batteries are not going to offer you value
until prices come down considerably (as we
predict they will) over the next five years.
For those who value independence from the
electricity grid, lithium batteries offer the
practicality of being lighter, and easier to store
and charge — and that’s before we look at the
dollars per watt equation.
You want your power to last longer. Lithium
batteries holds their voltage up higher
for longer and don’t suffer from that slow
downward spiral of the voltage that we all
know of with a lead acid battery. Devices
that need power draw a certain amount of
wattage (amps x volts) to operate.
Simple maths states that if you decrease the
voltage, the battery needs to supply more
amps to maintain the same power, which
means you will draw your available power
down faster (i.e., draw more amp hours).
While we are on capacity of lithium batteries,
some simple sums:
Recommended depth of discharge (DoD)
for AGM: 50 per cent.
Recommended DoD for LiFePO4: 80 per cent.
100Ah AGM battery: 50Ah.
100Ah LiFePO4: 80Ah.
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LITHIUM
BATTERIES
PART 4
The difference: 30Ah or 60 per cent more capacity.
Let’s look at the dollars and cents…
COSTS
Deep-cycle application: 100Ah, 50 per cent
DoD cycled daily.
Cost: 12V 100Ah AGM battery: $300; 12V
100Ah LiFePO4 battery: $1500.
Cycles at 50 per cent DoD: AGM: 650+;
LiFePO4: 6500+.
ROI on hardware: Will replace AGM
nine times before replacing LiFePO4
(9x$300=$2700).
Cost per usable kilowatt hour (kWh):
AGM: 12Vx50ah=600Wh x 650 cycles =
$300/390kWh = $0.77c/kWh
LiFePO4: 12Vx80ah=960Wh x 3500 cycles =
$1500/3360kWh = $0.45c/kWh
SUMMING UP
Now a Lithium battery is designed to be
discharged to 20 per cent remaining capacity.
You can see in the above that by using lithium
to its real capacity, and the massive number
of cycles they are capable of, that lead acid
batteries are 70 per cent more expensive
overall for each unit of energy utilised, and
that you would have had to replace your lead
acid batteries about nine times to meet the
same one lithium battery.
— BMPRO ambassador David Bayliss