Battery tenders?

[Grumpy]

Back in the 60's BR had a problem with the brake force of diesel locos restricting loads that could be hauled. The solution was to create brake tenders. These were basically cut down and shortened old carriages filled with concrete. Coupling these to the diesels provided more braking capability.
We currently seem to have a situation where there is a surplus of modernish EMU's (eg 350/2), some DMU's which are reaching life expiry, and a general wish to reduce running diesels under the wires.
Hence I wonder if it would be viable to take the original brake tender concept but fill with batteries rather than concrete. Then couple these up as required to an EMU with a power connection so that the EMU "thinks" it's drawing from the OHLE or third rail. I would have thought that this would be considerably simpler and cheaper than the work needed for the 769s.
Is this bonkers?

 

[Sun Chariot]

Back in the 60's BR had a problem with the brake force of diesel locos restricting loads that could be hauled. The solution was to create brake tenders. These were basically cut down and shortened old carriages filled with concrete. Coupling these to the diesels provided more braking capability.
We currently seem to have a situation where there is a surplus of modernish EMU's (eg 350/2), some DMU's which are reaching life expiry, and a general wish to reduce running diesels under the wires.
Hence I wonder if it would be viable to take the original brake tender concept but fill with batteries rather than concrete. Then couple these up as required to an EMU with a power connection so that the EMU "thinks" it's drawing from the OHLE or third rail. I would have thought that this would be considerably simpler and cheaper than the work needed for the 769s.
Is this bonkers?

I think the biggest gotcha, will be transfer to the EMU. BR(S) 27-way MU cables were for braking + driving controls. No DC power sharing unit-to-unit, due to the risk of electrocution to personnel.
EPBs initially built with power-jumpers but those were quickly removed; and the EPBs retained cab end power receptacles solely for "shore supply" provision at depots etc.

So - I think- a similar challenge would be faced here.

 

[zwk500]

Another challenge is whether they would be counted as a separate vehicle and therefore would need to be shunted to the rear or Marshalled between units or if they could be left on the same end for each return trip.

I can see the idea working in yards, if a class 18 isn't available.

 

[AF91]

I guess you could run two units semi permanently coupled together with a battery tender in between the two.

 

[Bald Rick]

Having such a tender at one end of the train implies either it having a cab or being shunted at termini.

Having it in the middle implies having it gangwayed where the units have gangwayed ends.

Both options imply platform length issues on some lines.

It would be far easier operstionslly, and almost certainly cheaper, just to put the requisite batteries underneath the unit - or if no space there, inside it. Space required for a 1MWh battery pack is roughly half the size of an accessible toilet.