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 type.
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 title.
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 batteries 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 curious!
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 purchase.
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 insulation products can prevent heat soak if the battery must be mounted close to an exhaust or turbo for instance. Specialised battery foam 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 or trays are available to suit most motorsport battery models. Sealed battery boxes are available if a standard wet lead acid battery is being used. Insulated terminal covers 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 cables can be made to suit. If there is room a conversion kit can be fitted to take standard type round post 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 tool 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 covers are available when not in use. The less common option is to use remote battery jumper posts, 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:
- 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.
- Monitor the voltage of the ODYSSEY battery with a good quality voltmeter until it reads 11.5-11.8V.
- 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.
- The charger needs to be of a minimum charge current capability as per the chart below.
- Plug the charger into standard wall AC power and start monitoring the battery voltage.
- Make sure the charge voltage at the battery terminals does not exceed 15.0V and continue charging for approximately 8 hours.
- 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 switch for good measure, and it is worth checking the voltage every few weeks.
Alternatively, a good battery conditioner 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
Lithium Ion 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 battery.
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.”!