Battery Talk


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. The following breakdown of specifications and terms will help you chose the correct type. 

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 wouldn’t 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. 

We have known issues of dead flat lithium batteries not being able to be recoveredAn expensive exercise! Something else you should think about is if you want to use a jump start battery on your car which is fitted with a lithium battery you will ideally need a second lithium battery to use as the jump battery, not the old car battery you had lying around previously!  

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. 



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. 
  1. Monitor the voltage of the ODYSSEY battery with a good quality voltmeter until it reads 11.5-11.8V. 
  1. 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. 
  1. The charger needs to be of a minimum charge current capability as described below. 
  1. Plug the charger into standard wall AC power and start monitoring the battery voltage. 
  1. Make sure the charge voltage at the battery terminals does not exceed 15.0V and continue charging for approximately 8 hours. 
  1. 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 measuret is worth checking the voltage every few weeks. 

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.” 


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