A Procedure to Determine the Actual Run Time Using Three (3) Lithium Manganese Oxide (IMR) or Lithium Nickle Manganese Cobalt (NMC/INR) 10440 (AAA) Size Batteries      Unfortunately, only the user can determine the actual safe run time without draining the battery too low. Almost every conversion to Dead Rail, battery on board, is unique to the locomotive and the actual track plan of the layout.      There are several factors and variables that make a specific, across the board answer, extremely difficult. Tools Required 1. A charger that can charge IMR or INR 10440 (AAA) size batteries to a charge termination voltage of 4.2V. (11/17/23 I now only recommend a Multi-Chemistry smart charger.) 2. A digital display voltmeter/multi-meter      Set up the preconfigured locomotive, battery car and the rest of the train on the actual layout for a prototypical run. Include all of the rolling stock for a prototypical running session, both behind the locomotive/battery car combination and at points to be switched, moved, etc. The battery car must have its battery boxes accessible.      Insert 3 10440 size, freshly charged IMR or INR batteries, along with an AAA shaped connector, into the slots of the two AAA battery boxes which are connected in series.      Start the LocoFi™ App and connect to the locomotive.      Do a prototypical run for thirty (30) minutes. Immediately remove a battery from the running circuit of the battery car and read its open voltage.      It is important to know that once the battery is removed from the circuit, the open circuit voltage of that battery will be steadily climbing, so measure the voltage as quickly as possible.      The open voltage cut off point is 3.5V for IMR batteries and 3.4V for INR.      If the voltage reads close to the voltage noted for the battery chemistry cut off voltage, the actual run time is 30 minutes.      If the voltage is over 3.6V for IMR batteries or 3.5V for INR batteries, reinsert the battery and continue running in 5 minute intervals until the measured voltage is near 3.5V for IMR batteries and 3.4V for INR batteries. That will yield the actual run time for the locomotive on the user's actual layout.      (Note: For MY portable demo layout and how I ran it prototypically, it took three (3) more 5 minute sessions for the 10440 size, IMR battery to reach the 3.5V cut off, a total of 45 minutes, to reach 3.545V, when measured as soon as possible after being removed from the battery box.)      For MY prototypical Actual Run Time, with MY locomotives (they are the same) and on my portable demo layout, the Actual Run Time was calculated at 45 minutes.)      Further testing on my "First HO Train Layout in a Long, Long Time" has shown that 55 minutes is possible using 3 Efest 350mAh IMR cylindrical batteries.