Turbine Engine Starting Notes;
According to Pratt Whitney, engine internal heating is cumulative in terms of engine life.
 GPU's always provide a higher voltage than the certified installed lead acid battery.
A lithium AeroStart Portable GPU provides 29 - 29 volts in initial starting voltage thus spinning the compressor faster resulting in more airflow, resulting in a cooler start (approx 100 degrees cooler ) which results in longer engine life making the purchase of an AeroStart lithium GPU a very worthwhile investment. This will reduce the cost / frequency of ship battery replacement and engine overhaul.
Two indicators of battery strength are; voltage drop during initial start and the amps needed from the generator in recharging the battery. A lead acid battery can take up to 20 minutes, a lithium battery would take less than 5.
Big voltage drop combined with big amps to recharge battery; bad ... low voltage drop with less charging amps, good.
Turbine washes can help.
A 28V Lithium AeroStart GPU will spool up the engine much quicker than the installed FAA certified lead acid battery, so be ready to push that fuel lever sooner. Especially true for helicopter GPU start and twin helicopter GPU start.