Re: Lawn mower not charging the battery when running

Paul,
 Yes there is a charging system. It is a bit lengthy to explain, but is the same for all small engines and lawn tractors. Google "small engine charging system" and you'll get some insight as to how they work.
or click on this link...
http://home.howstuffworks.com/home-improvement/repair/how-to-repair-small-engines3.htm
There are some things you'll need to diagnose the problem, like a digital voltmeter.
10 volts is definitely a problem, and I'm surprised you can get the PTO on at all.
Read over the link info and come back with any more questions.