Did some quick checking....
Tigress has 40k EP of power in normal operations.
I think 1 EP is about 250Mw?
I read that as the better part of 10 terrawatts for the power plant?

Earth as a whole ate about 19Tw of electric in 2012.

Most "detail oriented" Traveller stuff has the fusion plants charging
some kind of battery/capacitor system, which is used to even out
distribution needs to the ship systems.

If you presumed the fusion reactors were running up until the landing,
and then shut down, you'd have something like 400Tj of juice in the
caps. (40Tw x 1000 second space combat turn)

If all you're powering is lights, basic environment, and enhanced
environment, I suspect that would last a long, long time.

https://www.eia.gov/consumption/commercial/data/archive/cbecs/cbecs2003/detailed_tables_2003/2003set10/2003html/c14.html
 implies that very large buildings use about 17 Mw of power.  Figure
TL14+ has more efficient lighting and such, but also is running sewage
processing that our buildings don't do.

400Tj divided by 17Mw comes out to about 18 years before the batteries go dead.

If the ship's computer put the fusion plant into "hibernation" and
only fired it for a 10 minutes or so every year, I think it might last
a very long time. Maybe a 1 minute run each month.

That also leaves out the many-many subcraft. I'd imagine one could
pull the power plant from one of those, and use it to come up with the
measly 17Mw needed for housekeeping.