Take a look here --
http://www.sbs4dcc.com/tutorialstipstricks/esuloksound5keepalive.html - the answer may be hidden in here somewhere
I don't have ESU decoders .. but This may be relevant ..
Setting CVs - Enable Power Pack Control
When you connect an external capacitor or PowerPack, you are able to make the decoder switch off after a certain time. CV291/323/339 is responsible for that, since you are able to determine at what time the decoder is to switch off (as a multiple of 0.0328 seconds). You should set a time between 0.3 and 1.0 seconds to prevent your locos from driving too far during an emergency.
For the PowerPack to work, the function output responsible for the charge (typically AUX9 for LokSound, AUX7 for LokSound micro, AUX3 for nano) must be configured to the »PowerPackControl« function.
Set CV 31 = 16, CV 32 = 0 first, as required to address extended range CVs.
For LokSound 5, set CV339 = 31 (AUX9) Power Pack Control.
For LokSound 5 Micro, set CV323 = 31 (AUX7).
For LokSound 5 Nano, set CV291 = 31 (AUX3) and set CV353 = 0 to un-map AUX3 from F5.
Setting CVs 291, 323 or 339 to 31 is the proper way to set the LS5 for PowerPack Control. They are greyed out on the LokProgrammer because they are not function mapped. That is okay because they do not get function mapped to use them for PowerPack control so they will always be grey.
Just like the old V4, CV113 (found in the Driving Characteristics tab) controls the amount of time the PowerPack is active after the engine loses power.
Use that instead of CV325.
It is necessary to enable Power Pack Control in LokSound 5 model decoders in order to use the Keep-Alive function.
If Power Pack Control is not enabled, the keep-alive will be effectively turned off.
In LokProgrammer, LokSound 5 projects display a warning and link that when clicked, automatically sets CV315 = 0, thereby disabling Aux6.
Select projects do not display the warning or link but the CV value and results are the same.
For the PowerPack to work, the function output responsible for the charge (typically AUX9 for LokSound 5, AUX7 for LokSound 5 Micro) must be configured to the »PowerPackControl« function.
Set CV339 = 31 for LokSound 5 (AUX9).
Set CV323 = 31 for LokSound 5 Micro (AUX7).