Battery Conversion of Existing Stock

[stevieinselby]

Apart from low capacity batteries for shunting and hotel power, I can't see any likelihood of widespread conversion of existing trains to BEMUs.

• DMUs are the trains that would benefit the most from conversion to battery, but class 1xx types are not suitable as they have a mechanical drivetrain.
• DEMUs could be suitable but that's really only 22x Voyagers/Meridians, but they don't have an electric pick-up and they need to run looooong distances so would be difficult to manage in the short or medium term.
• EMUs are already running on fully electrified lines, so they don't need batteries to run in zero emission mode.
• Cascading older EMUs to run on non- or partially-electrified lines is a plausible use case, but (a) apart from the surplus 350/2s, they will still need to be replaced by new units themselves, so why not just buy new BEMUs for the lines that need them? and (2) conversion and repowering of older trains has not exactly been a roaring success so far.

The most likely conversions to battery bi-modes are existing diesel bi-modes, ie the 75x FLIRTs and 80x IETs, as these are routes that have a suitable drivetrain, a suitable electrical pickup for recharging at stations or on the move, and would benefit from being able to run more/all miles in zero emission mode. For HT and TPX (at least post-TRU), and some of LNER and GWR's fleet, conversion to full battery/electric should be viable – but significant works would be needed to install enough charging infrastructure to allow all LNER, GWR and AWC trains to ditch the diesel and run purely on electric or battery, and potentially changes to timetabling or rostering as well.

 

[InTheEastMids]

I would think that the fitting of batteries to tube trains would be regarded as somewhat negatively because, like all metro systems, trains have to keep to ultra-tight schedules with rapid acceleration/deceleration, so keeping the tare weight to the lowest possible would be the prime consideration. A minor point is that batteries heat up when in use, and the Underground has enough problems with rising temperatures as it is. On-shore batteries, now that's different.

I am not saying it's a show-stopper and it can't ever happen, but safety is a key issue.
The risk of battery thermal runaway / fire is very low. However, the potential impacts are very high. A train full of passengers, in a hard-to-evacuate, hard-to-ventilate tunnel environment, a battery system off-gassing harmful vapour, then the panic of passengers. Feels potentially disastrous.

The most likely conversions to battery bi-modes are existing diesel bi-modes

Agree there is a merit order of conversion, the Stadler units are the ones most obviously engineered with that in mind, followed by Hitachi.
If somebody was going to do a 22x, the time was now as the XC units go through refurbishment and the 222s cascade.

With something like the 350/2, if I was a train operator, I'd be saying, "We saw the 769 fiasco. Show us why it won't happen again".

Train owners don't seem inclined to do that work at risk (otherwise they'd surely have done it a while back).
To refurb to the standard of the EMR Connect 360 (which they probably need) looks like it'd be another £1.5m per 4 car unit / £375k per car on top of reengineering costs.

 

[anthony263]

Porterbrook have a opportunity to convert their class 350s to battery maybe even tri mode if you fit 3rd rail collection shoes.

Certainly they'd be good for GWR around the thames valley if they can still do 110mph under the wires

 

[mike57]

The risk of battery thermal runaway / fire is very low. However, the potential impacts are very high. A train full of passengers, in a hard-to-evacuate, hard-to-ventilate tunnel environment, a battery system off-gassing harmful vapour, then the panic of passengers. Feels potentially disastrous.

On a tube trains would supercapactors be a better way forwards, to ride out small gaps, and provide a 'get to the next station at low speed' capability in the event of power failure. They could also provide additional peak power in areas where the power supply is challenged. They have been used in trams, but as far as I am aware never in heavy rail. They could be a good fit for deep level tube.

 

[Zomboid]

Is that a real problem? How often do tube trains get stranded and people have to evacuate along the track? It seems to make the news when it does happen, which suggests that it's not common.

As for the idea of de-electrifying in favour of batteries...

 

[InTheEastMids]

Is that a real problem? How often do tube trains get stranded and people have to evacuate along the track?

Without much difficulty I was able to find the linked page below which I take it to mean there were 49 evacuations of tube trains in tunnels between 2004 and 2011, so maybe 7 per year is typical. So obviously incredibly unlikely it will ever happen to you (or me), but does appear to happen (no idea if it's become more or less common since then).

https://www.london.gov.uk/who-we-ar...estions-mayor/find-an-answer/tube-evacuations

On a tube trains would supercapactors be a better way forwards, to ride out small gaps, and provide a 'get to the next station at low speed' capability in the event of power failure.

It's a good idea if it turns out that loss of power is the key issue that prevents the train from moving.
The above link suggests trespass/person under train was the biggest single cause. I'm sure the power does get switched off, but obviously in that scenario there are other reasons why the train might not be able to move.

Porterbrook have a opportunity to convert their class 350s to battery maybe even tri mode if you fit 3rd rail collection shoes.

I agree it seems like a significant opportunity either alongside extension of GWR electrification or allow cascade of 387 into southern-land.
My earlier post was therefore speculating on why opportunities like this do not seem to be seizable!

 

[eldomtom2]

Also, I doubt batteries are going to allow for easy removal of drivers, since it's not like self-evacuation is allowed on unelectrified lines...

 

[Bald Rick]

I am not saying it's a show-stopper and it can't ever happen, but safety is a key issue.
The risk of battery thermal runaway / fire is very low. However, the potential impacts are very high. A train full of passengers, in a hard-to-evacuate, hard-to-ventilate tunnel environment, a battery system off-gassing harmful vapour, then the panic of passengers. Feels potentially disastrous.

There’s lots of battery trains in service now. Indeed every train has batteries on it in some form or other. This has all been fully risk assessed and deemed safe. And the risk is rather lower than, say, a DMU with 3000 litres of diesel (and some batteries!) on board.

 

[InTheEastMids]

There’s lots of battery trains in service now. Indeed every train has batteries on it in some form or other. This has all been fully risk assessed and deemed safe. And the risk is rather lower than, say, a DMU with 3000 litres of diesel (and some batteries!) on board.

The context of my post was specifically about London Underground moving from today's system to battery power...

I agree that moving from large tanks of diesel (plus small traditional batteries) to large lithium-based will almost certainly reduce incident frequencies and overall hazard.

There is still not much experience of incidents where there's a large lithium battery present, and is a very active topic based on incident response community I have talked to.
For confined spaces (e.g. LU tunnels) there is even less - the Austrians have done a couple of test fires, not aware that anybody else has.

 

[Technologist]

I would think that the fitting of batteries to tube trains would be regarded as somewhat negatively because, like all metro systems, trains have to keep to ultra-tight schedules with rapid acceleration/deceleration, so keeping the tare weight to the lowest possible would be the prime consideration. A minor point is that batteries heat up when in use, and the Underground has enough problems with rising temperatures as it is. On-shore batteries, now that's different.

See my many posts on how BEV vehicles can go faster than vehicles limited by ohmic losses/temperature in a conductor. See Model S Plaid vs Class 801 drag race for an example!

I have done some preliminary calcs on tube train batteries which I rationalised to 100, 200 and 300 KWh packs per carriage depending on the length of the line. These would add 1.9 - 5.8% to the train masses.

I would be surprised if any underground trains acceleration is capped by motors performance to the degree that a 6% increase in mass would make any difference. In the unlikely event that it would be we could always fit some improved motors and power electronics which if they were sourced from modern commercial of the shelf equipment would likely give you a weight saving too.

== Doublepost prevention - post automatically merged: 12 Jun 2026 ==

The context of my post was specifically about London Underground moving from today's system to battery power...

I agree that moving from large tanks of diesel (plus small traditional batteries) to large lithium-based will almost certainly reduce incident frequencies and overall hazard.

There is still not much experience of incidents where there's a large lithium battery present, and is a very active topic based on incident response community I have talked to.
For confined spaces (e.g. LU tunnels) there is even less - the Austrians have done a couple of test fires, not aware that anybody else has.

There are certified battery powered aircraft, the fire issue is more of an engineering and development challenge than a hard barrier. Also trains are likely to be using LFP types which are much more inherently stable and damage tolerant.

Also evacuation is somewhat easier when you have stripped out the 3rd and 4th rail, and the train can keep going even with major damage or if the power is interrupted.

The other key point is that we are looking at each train having 3 separate batteries per carriage. The safety case would be based on those batteries being in an enclosure that would be designed to stop a full pack fire from catching the rest of the train on fire (at least long enough to allow emergency response) and prevent a cascading failure.

The fire and smoke from a single 100KWh battery is likely to be well within the capability of the tunnel to duct away the smoke and heat and allow evacuation on foot.

 

[Snow1964]

Been announced today that first production batteries for Grand Central new trains are now being built.

But Headline also refers to removing 600 engines and replacing by battery packs, does that mean many of the IETs are getting batteries. Although I guess it could be for trains in other countries

Gateshead, U.K., July 15, 2026 (GLOBE NEWSWIRE) -- Turntide Technologies (Turntide), a global leader in electrification and hybridisation solutions and a long-standing North East manufacturer, received its first order from Hitachi Rail to begin production of its next-generation modular battery system for the first U.K.-manufactured battery trains for Arriva’s Grand Central.

First announced on July 2, 2025, this partnership involved an R&D component and has officially moved into production with the potential to support either new battery trains or retrofitting over 600 engines on existing Hitachi Rail U.K. fleets.

This new battery system will allow for lower cost of operations, extended range, and a path to zero-emission travel, while reducing reliance on fossil fuels and improving air quality and noise pollution. Turntide’s bespoke batteries are designed to deliver even greater power density in the same footprint of a diesel engine. This battery production is an advanced manufacturing milestone for Arriva’s Grand Central new fleet, which is being built in Newton Aycliffe, County Durham by Hitachi Rail.

This latest advancement in battery train technology follows a successful intercity trial which exceeded expectations in 2024. In a U.K.-first, the trial proved that Turntide’s battery system can be installed on Hitachi Rail trains to reduce fuel costs by 30% to 50% or deliver zero-emission travel in battery mode. This is especially important for improving air quality in and around stations that are not yet electrified.

“Following several years of close collaboration, we are now moving into production with Hitachi Rail to deliver quieter, more fuel-efficient, and environmentally friendly rail transport in the U.K.,” said Steve Hornyak, CEO of Turntide Technologies. “As operators and customers want to be less reliant on fossil fuels, we see growing global demand for hybrid and electric solutions in passenger rail.”

With roughly half of the global rail network still relying on diesel, tri-mode systems offer a faster and more cost-effective alternative to installing new electrification infrastructure, which can require significant time and investment.

North-East-Based Turntide Receives Initial Battery Production Order from Hitachi Rail for Arriva’s Grand Central Intercity UK Battery Trains

New batteries to enable greener train operations to remove over 600 engines on existing trains, offering lower cost of operations, more range, and path to...

www.globenewswire.com

 

[brad465]

Been announced today that first production batteries for Grand Central new trains are now being built.

But Headline also refers to removing 600 engines and replacing by battery packs, does that mean many of the IETs are getting batteries. Although I guess it could be for trains in other countries

North-East-Based Turntide Receives Initial Battery Production Order from Hitachi Rail for Arriva’s Grand Central Intercity UK Battery Trains

New batteries to enable greener train operations to remove over 600 engines on existing trains, offering lower cost of operations, more range, and path to...

www.globenewswire.com

The article says "or retrofitting over 600 engines on existing Hitachi Rail U.K. fleets.", so I don't think other countries are involved.

How many engines do each IET have? I believe the 9-car 800/802s have 5 engines each, so presumably a battery conversion for them would be removing 2-3 engines. 5-car units if retaining diesel capability I could see only having one engine replaced initially. 600 engines must easily be enough to do 1-2 battery units across the whole IET fleet; I also wouldn't be surprised if the 801s were to have their reserve diesel engine replaced by battery, similar to the 803s.

 

[zwk500]

But Headline also refers to removing 600 engines and replacing by battery packs, does that mean many of the IETs are getting batteries. Although I guess it could be for trains in other countries

The article you quoted says:

the potential to support either new battery trains or retrofitting over 600 engines on existing Hitachi Rail U.K. fleets.

So it would be IETs in the UK, but nothing has been ordered yet. As an interesting tangent, a rough calculation from info on wikipedia suggests there's 230 Bi-Mode units from the IET/AT300 family (including the 801s with the backup engine but not the 803 or 807), with 690 prime movers/gensets across the fleet, so not clear if potentially all bi-modes could be converted to BEMUs.

== Doublepost prevention - post automatically merged: 15 Jul 2026 ==

How many engines do each IET have?

9-car 800, 902: 5
9-Car 801: 1 (emergency only)
5-Car 800, 802, 805, 820 (GC units): 3
5-Car 801: 1 (emergency only)
5-Car 810: 4

Spoiler: Data:

Source: Wikipedia

Class	Number	Car	Engines	Num_Engines
800/0	36​	5​	3​	108​
800/1	13​	9​	5​	65​
800/2	10​	5​	3​	30​
800/3	21​	9​	5​	105​
801/1	12​	5​	1​	12​
801/2	30​	9​	1​	30​
802/1	14​	9​	5​	70​
802/2	19​	5​	3​	57​
802/3	5​	5​	3​	15​
803​	5​	5​	0​	0​
805​	13​	5​	3​	39​
807​	10​	7​	0​	0​
810​	33​	5​	4​	132​
820​	9​	5​	3​	27​
	230​			690​

 

[Zomboid]

The article you quoted says:

So it would be IETs in the UK, but nothing has been ordered yet. As an interesting tangent, a rough calculation from info on wikipedia suggests there's 230 Bi-Mode units from the IET/AT300 family (including the 801s with the backup engine but not the 803 or 807), with 690 prime movers/gensets across the fleet, so not clear if potentially all bi-modes could be converted to BEMUs.

== Doublepost prevention - post automatically merged: 15 Jul 2026 ==


9-car 800, 902: 5
9-Car 801: 1 (emergency only)
5-Car 800, 802, 805, 820 (GC units): 3
5-Car 801: 1 (emergency only)
5-Car 810: 4

Spoiler: Data:

Source: Wikipedia

Class	Number	Car	Engines	Num_Engines
800/0	36​	5​	3​	108​
800/1	13​	9​	5​	65​
800/2	10​	5​	3​	30​
800/3	21​	9​	5​	105​
801/1	12​	5​	1​	12​
801/2	30​	9​	1​	30​
802/1	14​	9​	5​	70​
802/2	19​	5​	3​	57​
802/3	5​	5​	3​	15​
803​	5​	5​	0​	0​
805​	13​	5​	3​	39​
807​	10​	7​	0​	0​
810​	33​	5​	4​	132​
820​	9​	5​	3​	27​
	230​			690​

Presumably there are a number of spare engine rafts around, and there would need to be a number of spare battery rafts too.

Replacing 1 engine on 5 cars, 3 on the 9 cars and the one on the 801s is a total of 299 engines (that includes the 810s, but not the 820s as that's not a replacement since they don't yet exist). So that's not how you get to 600!

 

[andy33gmail]

The risk of battery thermal runaway / fire is very low. However, the potential impacts are very high

The potential impact of having a few hundred or thousand litres of diesel is high too

 

[TrainViation]

Probably a really silly idea of me, but I'm guessing it wouldn't be possible to retrofit batteries on the Class 385 fleet also? As they are Hitachi stock, and have been mentioned to include the option later on when ordered by ScotRail.

 

[InTheEastMids]

The potential impact of having a few hundred or thousand litres of diesel is high too

Do LU trains carry hundreds of litres of diesel?
(Because that was the context you missed)

 

[Zomboid]

Do LU trains carry hundreds of litres of diesel?
(Because that was the context you missed)

Traction batteries on the tube would be madness. It's already fully electrified, the trains are necessarily pretty small, there are not insignificant losses incurred when putting energy into and out of storage and energy efficiency would be reduced by carrying the weight around. Never mind the fire hazard - which is a very different calculation in a tube tunnel compared to the main line (though lots of batteries at New Street would be an interesting risk assessment).

 

[martin butler]

I think that converting existing stock will only create more problems, than it solves, other than as test units to prove the system, and give real time feedback, the best option is to order units already designed as BEMU's with sub classes to operate either as overhead / battery for say GWR, and 3rd rail/ battery for Southern/SWR , some routes would need to change operator, for example Reading to Gatwick, should go over to either Southern, or SWR,In my neck of the woods, the Marshline could be operated by SE, but the units, would need to be able to operate with whatever else is being used, because it could also join/ detach with other services, at Hastings, or Ashford,

 

[pokemonsuper9]

I think that converting existing stock will only create more problems, than it solves, other than as test units to prove the system, and give real time feedback, the best option is to order units already designed

The existing Hitachi 8xx are likely to serve over 30 years more each, the TPE battery trial would have been a good test and I think I've heard on here it went positively, which leads the way for more to be installed across the 8xx fleet.

The deciding factor will be how much money Hitachi and Turntide want for the batteries and installation, and if the government consider it a good investment.
These aren't 30 year old EMUs like the 319s were, and it's the original manufacturer offering these batteries.

 

[martin butler]

The existing Hitachi 8xx are likely to serve over 30 years more each, the TPE battery trial would have been a good test and I think I've heard on here it went positively, which leads the way for more to be installed across the 8xx fleet.

The deciding factor will be how much money Hitachi and Turntide want for the batteries and installation, and if the government consider it a good investment.
These aren't 30 year old EMUs like the 319s were, and it's the original manufacturer offering these batteries.

Trouble is though, the most likily units will have to be Alstrom designs, based on what's being produced now, or a modernised version of the 377/8/9 family because that's what's in use by GWR, Southern/ SE, and these won't be replaced any time soon unless some units can be converted during a heavy overhaul and rebuilt because any unit will have to be able to couple with other units during normal service, for example on the GW ,a battery unit might have to work a Paddington local, with a non battery unit, and on Southern, trains divide en -route, and others join,

 

[andy33gmail]

Do LU trains carry hundreds of litres of diesel?
(Because that was the context you missed)

Only a few: https://en.wikipedia.org/wiki/London_Underground_diesel_locomotives

I’ll quote more carefully in future. The thread itself had a wider scope

Never mind the fire hazard - which is a very different calculation in a tube tunnel compared to the main line

 

[InTheEastMids]

I think that converting existing stock will only create more problems, than it solves,

These aren't 30 year old EMUs like the 319s were

Retrofitting batteries to modern stock brings its own complications in that there is so much more dependence on software integration. Hitachi are doing it themselves in a train platform that's currently in production. That also gives you 25 or more years of service to recover the investment.

But thinking about all the (mostly) Siemens & Bombardier stock that are now 10-25 years old and may only have 15-20 years left, I think it's more technically risky with lower benefits and it won't happen.

 

[pokemonsuper9]

But thinking about all the (mostly) Siemens & Bombardier stock that are now 10-25 years old and may only have 15-20 years left, I think it's more technically risky with lower benefits and it won't happen.

Yes I imagine fitting batteries to (for example) some 377s to go to Uckfield would be more difficult than fitting them to TPE 802s which have already had a working prototype and at this point - a supply chain too!

 

[stevieinselby]

Probably a really silly idea of me, but I'm guessing it wouldn't be possible to retrofit batteries on the Class 385 fleet also? As they are Hitachi stock, and have been mentioned to include the option later on when ordered by ScotRail.

What would be the point? There's no shortage of demand for the 385s (and 380s, 334s, 320s and 318s) to run as pure EMUs.
Much better to keep existing EMUs running on electrified routes, and buy new purpose-built BEMUs to replace the 15x units on routes that are not fully electrified.
Retrofitting batteries onto EMUs is worth considering when you have surplus EMUs that have no other useful deployment, but other than that it adds unnecessary complications, and given that we need new build units anyway then the sensible thing to do is to make those the BEMUs, which are pretty universally more reliable than retrofits.

 

[InTheEastMids]

What would be the point? There's no shortage of demand for the 385s (and 380s, 334s, 320s and 318s) to run as pure EMUs.
Much better to keep existing EMUs running on electrified routes, and buy new purpose-built BEMUs to replace the 15x units on routes that are not fully electrified.

Agree. Existing EMU will only work when
1. There is not enough pure EMU work
2. The platform and train is new and suitable enough for an OEM to do the work. That gives suitably low risk and long lifetime to help the economics.
3. Other interventions like a significant refurbing of the interior for a different role isn't required (as this significantly increases conversion costs)

Off the top of my head the only trains that tick all boxes are Hitachi IC and Stadler bimodes

 

[brad465]

Now we know TPE is getting new BEMUs that will serve Hull among other destinations, I think Hull Trains' 802s would be prime for battery conversion. If OHLE is being installed at Hull, then the 802s should easily have enough charge to get from where they leave the ECML to Hull, then charge up while there to ensure they get back (and charge up in the overnight sidings if also electrified).

 

[Bald Rick]

Now we know TPE is getting new BEMUs that will serve Hull among other destinations, I think Hull Trains' 802s would be prime for battery conversion. If OHLE is being installed at Hull, then the 802s should easily have enough charge to get from where they leave the ECML to Hull, then charge up while there to ensure they get back (and charge up in the overnight sidings if also electrified).

It will be interesting to see what happens there. The investment case for that will rely on the cost of conversion being offset by the lifetime cost savings of maintenance and energy saving.

 

[Zomboid]

If Hull, Scarborough and Saltburn are operated by the new trains and Cleethorpes sticks with 185s, won't the rest of the TPE network (operated by 802s and 397s) be fully electrified?

They could just take the diesels off the 802s and run them as straight electric units, no need to mess about with batteries.

 

[Bald Rick]

They could just take the diesels off the 802s and run them as straight electric units, no need to mess about with batteries.

They will need off wire capability for the regular diversions via Castleford / Brighouse / Hebden Bridge / etc.