Battery Basics

Battery Basics

Battery Basics Explained - Battery101

Here we cover some of the basics of Battery Traction in railways, in a simple bite-sized way.

This area is under development at present so please check back to see new content as it is published. If you'd like to see a topic covered then drop us a line via the form. 

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These articles are not going to be detailed - just enough to give a basic overview. If you need the detail then contact our experts

Where does Battery Traction Fit?

Diesel may have many good points as an energy carrier to deliver traction power which is why its use is so common, but it also has uncomfortable problems in terms of air-quality and CO2 emissions. With an increasing focus on climate change and decarbonisation of transport, people, companies, and countries increasingly wish to seek out lower carbon fuels as alternatives and battery power is one option which you will increasingly see as well as hydrogen. Which choice for traction is right? Our teams can help answer this question and you can see an example of a project we completed here studying traction options for routes in the Netherlands.

There are many permutations of use cases for battery traction - we will only cover some here to illustrate some options available.

  • Extending electric operation beyond wired sections.  This allows battery hybrid trains to operate beyond the end of the wires perhaps on a secondary/branch lines and to recharge whilst on the section of electrified route avoiding costly full route electrification. It can also be used to provide last mile connectivity for freight vehicles allowing short distances to be covered on non electrified track such as sidings.  (Example)
  • Pure battery power. Typically suited for lower traffic densities on more lightly used and relatively short passenger routes, this 100% battery operation charges at strategic points along or at the end of the route. 
  • Urban air cleanup. Where urban air quality requires improvement, electric power can be utilised on a last mile basis into and out of urban locations using internal combustion engines as a range extender between urban locations. (Example)

Battery Benefits

  • Zero (in-use) emissions

  • Potential to utilise renewable energy for low/no carbon emissions
  • More energy efficient than internal combustion engines
  • Noise and vibration improvements over internal combustion engines
  • Lower maintenance (compared to diesel)

Battery challenges

  • Lower energy density than diesel or hydrogen​
    • More space/weight required for batteries to deliver same range (practical range currently restricted to around 100km, significantly less than diesel or hydrogen)
    • Long distance freight use is currently not feasible on just battery power
  • Lower energy efficiency than overhead electrification
  • Charging times (depending on application)
  • New charging infrastructure may be needed (depending on application)
  • Thermal management often required (performance is affected by temperature)
  • Cost

Decarbonising Transport

Where the battery revolution on our roads is progressing, we see an emerging picture where battery powered transport can slash the CO2 emissions by approximately two thirds when compared with traditional diesel internal combustion engines. 


The figures above from the UK, whilst imperfect in the way they compare transport mode occupancy, they do highlight the six-fold disparity between emissions from UK national rail (majority diesel powered), and international rail (electrically powered from a low carbon grid).  In both car and rail cases, electrically powered transport has far lower emissions than its fossil fuel equivalent, and we are increasingly aware that carbon counts. 

Other Battery Benefits - It is not all about decarbonisation

The swap to battery traction, aside from reducing the carbon intensity of transport often yields co-benefits which can be just as important.

  • Swapping to battery power reduces noise levels and improves local air quality significantly. Even a hybrid approach using diesel or biodiesel engines as a range extender delivers significantly improved urban air quality with reduced noise levels for rail-side neighbours. Where local or national air quality legislation enforces the clean-up of city air, then battery power is becoming a go-to solution in both road and rail industries.  Here is an example.
  • Flexibility of operations can also be improved when utilising battery traction, particularly where electrification is present along only part of a route. The ability to operate beyond the end of the wires can free previously captive fleets delivering enhanced flexibility of operations. Even in the traditionally battery adverse freight arena, battery last-mile capability is a valued asset on freight locomotives allowing greater autonomy in port and freight sidings. Here is an example.

Battery power express

Battery technology has moved on at great speed during the last generation. We have seen battery powered road vehicles evolve from the leisurely lead-acid milk float to today's speedy lithium supercars.

Over the same period we have also seen the cost of energy storage dramatically fall. Lithium-ion battery cost has decreased by 97% in the last 30 years turning it from an expensive novelty to widespread use around virtually every home. 

Battery cost graph showing steep decline over last 30 years of 97%25

In combination with this revolution in both price and performance, we are emerging into an ever more climate conscious world. The focus on decarbonisation to avert climate disaster casts a spotlight on improving transport emissions in all areas. Transport energy use accounts for approximately one quarter of global CO2 emissions and has not enjoyed the same pace of CO2 emissions reduction as other sectors, due to the challenging nature of the on-board engergy requirement for vehicles.  

Charging ahead - Different philosophies for battery operations

To utilise battery power, the recharging of power back into the batteries can be just as vital as using that power to drive vehicles. 
There are many different opportunities to put power back into batteries and we briefly discuss a few here:

  • Depot charging - In a similar way to EV cars, when the rollingstock returns to its depot it is "plugged" in to recharge the batteries typically overnight. This whilst relatively simple to implement does require battery packs that are large enough to cover the entire days milage which depending on route and usage may be impractical. This method may be combined with other recharge options.
  • Under the wires charging - Where routes are partially electrified, there is the option of drawing power from electrification (overhead or 3rd rail) to both power the hybrid vehicles and recharge their batteries at the same time. 
  • Opportunity charging - This method uses opportunities during the normal vehicle operations to charge batteries, typically at station termini or at stations where a significant dwell time is planned. 
  • On-Board charging - This utilises other power sources already onboard the vehicle to charge the vehicle battery. A typical situation is where a hydrogen fuel-cell provides power to a battery which powers traction motors. In periods of low traction power demand, the fuel-cell provides power to recharge the battery. Another option is to use diesel or other power sources to provide a range extension solution where required.
  • Regenerative braking - As there is a significant weight in a rail vehicle the opportunity exists to recuperate energy from braking to charge the battery to reduce the power requirement for a journey. The opportunities for regenerative braking are dependent on the route characteristics. 

We hope you have found some of these battery basics topics useful

If you have a battery project which are considering then contact our experts to see where we can help.

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