RV FEATURE
PARALLEL
UNIVERSE
THERE HAS ALWAYS
BEEN CONJECTURE
ABOUT WHERE IT IS
POSSIBLE, OR EVEN
SAFE, TO WIRE LITHIUM
BATTERIES IN PARALLEL.
LITHIUM
BATTERIES
PART 6
Is it possible to wire lithium batteries in
parallel? The argument that it is not possible
concerns the fact that inside each lithium
battery is a battery management system
(BMS), and with multiple batteries in parallel,
they may compete with each other, as they
are not programmed to understand that there
are other batteries in the ‘bank’.
The BMS manages many electronic
parameters that enable the 3.2V internal cells
to operate together as a 12V battery and they
are not all created equal.
The BMPRO batteries are very suitable for
configuring into a larger bank of batteries to
provide a higher amount of available amp-
hours for campers who either have a high
energy requirement or intend to not have
access to charging capabilities for some time.
Up to four BMPRO lithium batteries can be
installed in parallel. As per good practice with
lead-acid setups, all batteries should be of the
same brand, size and age. Once properly wired
in parallel, this bank should now be treated as
just one big battery, still of 12V but maybe now
200 or 300Ah in capacity. Some advice:
1 Use the same brand, size and age of
batteries when paralleling.
2 Ensure all batteries are individually fully
charged with an open circuit voltage (the
measure of energy potential between the
62 \
positive and negative) after being rested
(not on charge for at least one hour), and
with no loads connected within 0.2V of
each other. To do this, charge the batteries,
let them rest for at least an hour and,
using a multimeter, check that the voltage
range of the batteries does not different
by greater than 0.2V. This will prevent the
overuse of one or more of the batteries.
3 Ensure cable of sufficient capacity is
installed and all connectors are capable of
carrying the increased amperage. Ensure
cable lengths are all of the same length.
4 Positive and negative should be at
opposite ends of the bank. Don’t run the
positive and negative from the one battery.
5 Install a suitable fuse on the positive cable
(between the last terminal and the load)
close to the terminal for ease of access.
6 Recharge the system every three months.
7 One of the most critical points that must
be considered when paralleling lithium
batteries is that if the system is not sized
and configured properly, one battery
could enter ‘protection mode’ due to deep
discharge or over-discharge current. This
battery would then sit idly and put more
pressure on the other batteries.
— BMPRO ambassador David Bayliss