I'll add one point.
If they have a battery, Replace it, then Charge it overnight before running the engine.
A battery that is several years old is suspect right off the bat.
Old MTH batteries are best tossed out. Current production no longer uses them but I have several old PS1 and PS2 engines that get a battery check as soon as they come out. The PS-1's batteries have been changed out.
I do not use BCR's tho many swear by them.