I am no expert but I have a few ps1 engines that I have had very few problems with. your best bet is to get a a new battery from your local hobby shop and install it. then set the engine on the track and power it up in neutral/startup mode to at least 12 volts and let a charge for a few hours (at least 3 but now more than 8). If you can't get an mth battery than you can temporarily use a standard 9 volt battery to test the loco. After that just remember that ps1 is basically a conventional engine with a nice sound system. So run it like a conventional engine because if you try to start out at 18 volt like a ps2 or ps3 engine it will take off like a shot.
I hope your new engine works out well
JZ.