My preferance is to go for a 12 volt geared starter and get a 18 volt lithium iron battery pack out of the new generation cordless drills, mount the batteries into a jiffy box and attach to your geared starter.
It will start the 170 with no problem at all, the only down side is that your 170 can be idiling away and you are still cranking it with the starter thinking when are you going to fire.
The Magnums are cheap enough to replace if you eventually burn it out.
But I have never burnt one out as the brushes usually wear down first and I cannot find replacement brushes here in Aust, so I have a couple of good starters just waiting for brush's.
The other big down side is that everyone at the field will borrow it as it is so good, but the lithium iron batteries do last quite a while before charging is required, just as well when everyone borrows it.

XMANS