Professional BoatBuilder - December-January 2018

DECEMBER/JANUARY 2018 37

SYSTEMS: Battery Technology

operating in high ambient tempera-

tures, defects in manufacturing, exter-

nal heat, and physical damage. Several

of these conditions are not uncom-

mon in marine applications. What’s

more, whereas in automotive and

other mass applications, the battery

builder and installer have near com-

plete control over the installation for

its entire life, once a boat is in the

hands of its owner, there is no telling

who will mess with the installation

and wiring over the life of the boat.

To ensure the safety of lithium-ion

batteries in the boating world, a

sophisticated battery management

system (BMS) is required that, at a

minimum, monitors voltage and tem-

perature at the individual battery cell

level, and has mechanisms to shut the

battery down if it is abused or if any

one cell begins to drift outside

when disconnected from charging

sources and loads. Once initiated, this

exothermic reaction can be hard to

stop, resulting in a rapid temperature

rise—the above-mentioned condition

known as thermal runaway. Depend-

ing on the chemistry, the battery may

get hot enough to set itself on  re (as

happened on some Boeing airplanes),

but even if the chemistry cannot get

this hot, there will be a pressure rise

that frequently leads to venting of the

electrolyte. If there is any ignition

source, the electrolyte will catch  re,

which generally cannot be put out.

 e normal result is the loss of the

boat.  ere have already been a num-

ber of such boat losses.

Conditions that can initiate thermal

runaway include overcharging, over-

discharging followed by a recharge,

charging in freezing temperatures,

Lead-Acid to Lithium-Ion

Nothing on the horizon suggests

lead-acid batteries will absorb the

kind of charging currents I would like

to throw at them up to high states of

charge and at e ciency levels that will

limit the internal heat generation in

the battery. For this, the only game in

town is lithium-ion.

Lithium-ion batteries have several

times the energy storage capacity of an

equivalent volume and weight of lead-

acid batteries, can be charged at

extraordinarily high rates of charge to

very high states of charge, can be

almost totally discharged hundreds of

times to thousands of times without

damage, are immune to sulfation, and

as such can be operated permanently

in a partial state of charge. As noted

above, the most e cient lead-acid

batteries (AGM) are only 85% e cient

at converting electrical energy into

chemical energy and vice versa, while

lithium-ion chemistry is more than

95% efficient, resulting in far less

heat generation during high-rate dis-

charges and recharges—an important

consideration in our high charge rate

experiments. This is an amazing set

of positive characteristics.  ere are,

however, some potential negatives.

Preventing Fires

Every lithium-ion battery currently

in the marine marketplace contains a

 ammable electrolyte. And all lith-

ium-ion batteries can be driven into

an exothermic state, in which the bat-

tery generates heat internally even

He also tested an early-generation lithium-ion battery in his garage.

Far left—Highly promising

lithium-ion batteries, shown

here in an early-generation

onboard installation, can with-

stand the increased energy

 ows. Their chemistry is more

than 95% ef cient, generating

much less heat during high-

rate charges. Left—To

research which type of marine

batteries can withstand a high

rate of charge, the author

included diagnosing a TPPL

battery by sawing it apart.

BRUCE SCHWAB

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