How to Choose and Maintain a Motorsport Battery

In 1749, Benjamin Franklin, the U.S. founding father,
first used the term “battery” to describe a set of linked capacitors
he used for his experiments with electricity. These capacitors were charged
with a static generator and discharged by touching metal to their electrode.

Linking them together in a “battery” gave a
stronger discharge. Originally having the generic meaning of “a group of
two or more similar objects functioning together”, as in an artillery
battery, the term came to be used where many electrochemical cells were
grouped. Today even a single electrochemical cell, e.g. a dry cell, is commonly
called a battery.

The automotive use of the battery started in the 1920’s
when the electrical starter came into use in place of the mechanical starter
handle. The battery allows the starter to operate and powers the ignition
system before the engine is turning over fast enough for the engine to fire.
This will typically take around 3% of the battery capacity and the charging
system then takes over, which – in most cases – is an alternator. The battery
also gives extra power where the electrical load is more than the output of the
alternator for short periods.

Types of battery and terminology

There are a large range of batteries available in many
sizes, capacities, weights and types. The choice can be rather bewildering and
if you get it badly wrong you might have to buy another or carry around twice
the size of battery you require!

Battery selection for motorsport is a compromise of
having enough capacity but not carrying more weight than necessary, and the
following breakdown of specifications and terms will help you chose the correct

AH Rating

An amp hour (AH) is a rating usually found on most automotive batteries. The standard rating is an amp rating taken for 20 hours. What this means for a 100 AH rated battery is this: Draw from the battery for 20 hours, and it will provide a total of 100-amp hours. That translates to about 5 amps an hour. (5 x 20 = 100). However, it’s very important to know that the total time of discharge and load applied is not a proportional. As your load increases, the actual capacity will decrease. If you discharged that same 100 AH battery with a 100-amp load, it will not give you one hour of discharge. On the contrary, the perceived capacity of the battery will be less. The AH rating is a useful guide to allow comparison between different batteries.

CCA / PCA Rating

Cold cranking amps (CCA) is a measurement of the number
of amps a battery can deliver at 0°F (-18 degrees C) for 30 seconds and not
drop below 7.2 volts. This rating gives a good indication of the current
available, especially useful for tuned high compression engines.

Again, this allows different sizes and types of batteries
to be compared. Some batteries are rated by PCA rather than CCA. Unlike CCA the
pulse cranking ampere (PCA) rating does not have an “official”
definition; however, it is believed that for true engine start purposes a 30
second discharge is unrealistic. With that in mind, the PCA is a very short
duration (typically about 3 seconds) at a high rate of discharge. As the
discharge is for such a short time, it is more like a pulse hence the rating

Lead Acid batteries

The most common automotive battery is a lead acid type.
The battery consists of alternate plates made of a lead alloy grid filled with
sponge lead (cathode plates) or coated with lead dioxide (anode).  This is typically known as a wet cell battery
and this needs to have a robust and typically heavy case to contain the
corrosive electrolyte and prevent the plates short circuiting. The standard
lead acid battery with electrolyte will need fitting in a battery box for motorsport
use to prevent leaks and need to be fitted upright.

Most motorsport
are also lead acid, but these use a different type of
construction. The lead plates are normally a much purer lead – some as much as 99%.
This allows the plates to be thinner and more can be fitted in the same area
giving extra surface area and therefore more power. The liquid electrolyte is
replaced Absorbed Glass Mat (AGM) technology to contain the acid.

AGM batteries differ from conventional liquid lead acid
batteries in that the electrolyte is held in glass mats. Very thin glass fibres
are woven into a mat to increase the surface area enough to hold the
electrolyte on the cells for the battery lifetime. The absorbed acid means
there is no chance of any leakage. This means AGM batteries can be installed
upright or on their side and this technology also allows the plates to be more
densely packed resulting in a more compact battery and the smaller case further
reduces weight.

The pure lead and extra surface area allow the motorsport
AGM batteries to create a lot more power than the equivalent wet cell standard
type battery. The AGM mats also mean the lead plates are held more securely and
better resist shock and vibration ideal for harsh competition environment. The Odyssey
and Varley
brands are the best-known suppliers of motorsport AGM batteries.

The advantages of lead acid batteries include the price,
vast range of sizes and power ratings and their compatibility with standard
chargers. It is a generally well-known and understood technology.

Lithium Ion batteries

Motorsport batteries are normally Lithium Iron Phosphate
or LiFePO4. This is widely recognised as the safest Lithium Ion technology
currently available.

The lithium iron phosphate battery (LiFePO4 battery) uses
LiFePO4 as the cathode material, and a graphitic carbon electrode with a
metallic backing as the anode. The chemistry is probably rather too complicated
for the subject of this blog, but many resources are available if you are

This battery type has advantages over a lead acid battery both wet cell and AGM types. The weight is the biggest feature, swapping for a similar power can be one third of the weight. The cycle life (amount of charges and discharges) is longer for Lithium Ion like for like, and the recharge time is shorter. The batteries are much more tolerant to deep discharge than lead acids types. The downsides are cost although this can be offset against the better cycle life. The performance at lower temperatures (generally below around – 10 degrees) due to the chemistry will be less than the comparable lead acid battery but this not much of an issue for the majority of motorsport.

Motorsport UK only allow use of batteries registered with
them that conform to UN38.3 Classification so this should be checked before

Battery Selection Checklist


The space available needs to be checked, especially if
relocating for better weight distribution. The size of the mounting bracket
will also have to be accounted for. In most cases a motorsport battery AGM will
be smaller than the original.  The AGM
and Lithium batteries can also be laid on their side or end to give more
mounting options.

Cold Cranking Amps (CCA) or PCA

The cranking amps available needs to be checked to ensure
it is enough for the power of the starter motor being used. The following rough
guide can help:

  • Summer Starting (Petrol): 150-200A
  • Summer Starting (Diesel): 450-550A
  • Winter Starting (Petrol): 250-350A
  • Winter Starting Diesel: 700-800A

The rating can be lower if used with a slave starter
battery or starter jump pack, but this can be a risk if a few restarts are
needed while competing.

Ampere Hour Rating (AH)

The AH rating is a guide to how much capacity the battery has. A motorsport car can generally get away with a lower rating than a road car. The road car in winter can have current drawn from lights, heater blower, wipers, heated rear window (and mirrors), in-car entertainment, heated seats and plugged-in chargers which might all be switched on at the same time, this is extremely unlikely in a motorsport car.

The current draw of the components in use will need to be
calculated and an appropriated AH Rating selected. A car with no charging
system, total loss of electrics, will need to make sure the capacity is enough
to cover a race and leave a bit in reserve for any restarts. If the car is
likely to race twice in one meeting and there is no chance to charge the
battery this will also need accounting for.

The exception to reducing the AH rating compared with the original may be a rally car / off road racer with light pod and trip computer, map light, heated windscreen, intercom and radio, but in most cases an uprated alternator will take care of this. The rating of the alternator fitted will need to be checked against the likely load of all these accessories, and a battery chosen accordingly.


A battery does not like excessive heat or vibration so
thought should be given to where and how the battery is mounted. Heat
products can prevent heat soak if the battery must be mounted
close to an exhaust or turbo for instance. Specialised battery
will prevent damaging vibration effecting the battery.


A battery must be secured so it does not come loose in an
impact or allow the terminals to earth on surrounding metalwork. Ready-made
tailored battery brackets
are available to suit most motorsport battery models. Sealed battery
are available if a standard wet lead acid battery is being used.
Insulated terminal
will prevent any accidental shorting.


Race batteries almost all use a M6 stud or bolt to secure
the terminals. The correct crimp
/ solder terminals
are available to fit to existing cables or new
can be made to suit. If there is room a conversion
can be fitted to take standard type round
battery terminals. Quick
release terminals
are also available if a quick changeover is required.
Care should be taken when tightening batteries terminals and the manufacturers
torque setting adhered to.

A useful tip if you wish to make crimped battery ends but
do not have a crimping
is to use a centre punch in the centre of the clamp tail to crimp the
cable in place. Remote connection to the battery can be very useful if the
battery is located under hard to remove panels or bodywork or starting by a
slave battery or jump
starter pack
. If using for just charging this can be achieved by connecting
a lead available from most of the battery conditioner manufacturers. This will
allow simple connection and can be left in place. If using the remote
connection for starting, then a much heavier connection will be required. This
is achieved typically by using the well-known Anderson
jack plug
. This is a quick release electrical connection that can take the
full current for starting. One half of the connection will be bolted
permanently to the car and the other half connected to the slave battery or
jump start pack. When disconnected no current will flow. Protective
are available when not in use. The less common option is to use
remote battery jumper
, these will need covering after starting or charging to prevent any
accidental discharge.

Battery Care & Maintenance

Lead acid batteries 

A race battery costs considerably more than a
conventional battery so it pays to have a good maintenance regime. The battery
should always be fully charged after use as a battery that is regularly put
away with a low state of charge will eventually sulphate the battery plates.

This can be sometimes be recovered but not always. Many
batteries returned under warranty are not faulty and just not cared for
correctly. The following procedure to recover deeply discharged AGM batteries
by ODYSSEY® batteries is very useful:

For safety reasons, many 6V/12V automotive/commercial type chargers will not turn on when an attempt is made to charge any style 12V battery that has a very low open circuit voltage (OCV). For example, a charger set for 12V charging connected to a 12V battery that has an OCV less than 4-5V, the charger senses it is connected to a 6V battery (which it is not) and will not initiate a charge because it is set for 12V charging.

Your ODYSSEY battery has very high recharge efficiency and is robust enough to accept a charge even when its OCV is less than 5.0V. If the charger’s output voltage does not rise above 15.0V the following procedure should allow you to bypass the charger’s safety circuit and safely attempt to recover (charge) the ODYSSEY Battery.

One note: ODYSSEY batteries that have been operated over a prolonged period and have not routinely been charged back to near or full charge will have developed sulphated oxide and can be more difficult to recover. In some cases, if the sulphation condition is well developed, especially overtime, it may not be possible to achieve full capacity. This condition is not a warrantable claim as it is not the result of a factory manufacturing defect but abuse or neglect in the application. With the charger connected and even though the battery has a low OCV and the charger does start up, then a full recharge should be attempted. Monitor the battery temperature and if it should get hot to the touch (125+°F, 51°C), then stop charging and allow the battery to cool. Once at room temperature, reengage charging and allow to fully charge. Test for capacity and if still low, discharge to 10.0V and recharge again and retest.

If the charger will not engage, the following procedure can be used:

  1. Using jumper cables connect the positive terminal of a healthy battery to the positive terminal of the dead ODYSSEY battery; then connect the negative terminal of the healthy battery to the negative terminal of the ODYSSEY battery. If you are using the battery in a car, do not run the engine during this operation.
  2. Monitor the voltage of the ODYSSEY battery with a good quality voltmeter until it reads 11.5-11.8V.
  3. Disconnect the jumper cables on the ODYSSEY battery, then quickly connect the positive cable of the charger to the positive terminal of the ODYSSEY battery; then connect the negative cable to the negative terminal of the ODYSSEY battery.
  4. The charger needs to be of a minimum charge current capability as per the chart below.
  5. Plug the charger into standard wall AC power and start monitoring the battery voltage.
  6. Make sure the charge voltage at the battery terminals does not exceed 15.0V and continue charging for approximately 8 hours.
  7. Disconnect the charger and allow the battery to sit open circuit with no connections for 12 hours or install the battery and turn the headlights on for 2 minutes to remove the charging surface charge voltage. Turn the headlights off, allow the battery to rest for a few minutes and read its voltage. A fully charged ODYSSEY battery will read 12.84V verifying a full charge.

Battery Models Minimum Charging Amperage PC310 – PC680 6 amps*, PC925 – PC1200 12 amps*, PC1220 – PC1750 25 amps*, PC1800-PC2250 50 amps.*

(* Recommended
charging amperages are for single (boost) recovery charge cycles, not for
repetitive deep cycle charging)

A race battery fully charged and fully isolated can keep
a charge much longer than a conventional battery due to its low internal
resistance. If you are unable to keep the battery on a maintenance charger it
is best to fully charge the battery and then disconnect the terminals and
switch off the master
for good measure, and it is worth checking the voltage every few

Alternatively, a good battery
will both fully charge and maintain the charge while the car is
stored. Again, it is worth checking
the voltage
periodically to check it is being maintained correctly, some
cheaper brands do not fully charge the battery. A battery conditioner is a
multi-stage charger that will analyse the battery, charge to full charge, hold
at full charge for several hours to “condition” the battery (hence the name)
and then have an auto maintenance mode that checks and charges if the voltage
drops below a set level.

Many chargers have lights or displays to show the battery
state. If a car has a hard to reach battery, many of the manufacturers offer remote
connection leads
so the charger can be attached easily and quickly. These
leads can be left in place permanently, some of these show the state of the
battery via built in warning lights. These draw a tiny current so will have a
negligible effect on battery charge.

Lithium Ion batteries

batteries need a charger made specifically for this type of battery.
These batteries charge much faster than lead-acid, typically fully charged
within an hour. A multi
stage charger
is worth using as this will monitor and maintain the battery
when not in use. If it is not possible to connect to mains power, then it is
best to charge the battery after last use and then leave completely
disconnected. A Lithium battery will hold a charge much longer than a lead acid

In summary

A motorsport battery will provide easier starting and will save weight and space compared with a standard wet cell lead acid battery. Careful selection of the correct battery using the above guidelines above will mean the right battery for the job. A good maintenance regime will keep the battery in top condition and will save unnecessary costly replacement. A small part of a competition car but very important, we hope you find this guide “electrifying” and keeps your battery knowledge “current.”!

The post How to Choose and Maintain a Motorsport Battery appeared first on Demon Tweeks Blog.

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