Mike
I multi-purpose my batteries as well. Been playing with RC toys for many years, long before I equipped trains. I use the same batteries for my electric airplanes/trains today. Raced cars/trucks/boats and garnered lost of experience with NiCad batteries therein. Lithium batteries were not viable at this time for these applications and NiMH had recently been introduced to this market (pre 2004). We started using Lithium Ion cells for flight power systems in Giant Scale RC planes, again garnered/learned a lot about this new technology in short period of time. About the same time Li-Po batteries became available in smaller capacities, my son and I delved heavily into small flat foam Depron RC planes equipped with Li-Po’s, Josh designed many of his planes and competed nationally with same. Several years later Li-Po’s evolved into the beasts of the battery world.
In my experience NiMH cells are viable but lacke resilience and lived a short life as compared to their brethren NiCD.
That said if your NiMH cells are still capable of delivering near their rated capacity (5000mAh) and will sustain rated voltage under load (unlike Li-Ion) calculating the run time knowing the current requirements plays out like:
5000mAh / 1000 = 5 Amps over 60 minutes
Estimated current draw for LGB Mogul/lights/RC = 1.5 Amps
5Ah/1.5A = 3.33 hours
Michael