925 delayed start, no start or clatter but not engaging

Understand this could be a weak battery, but has progressed to only random starts after turning key multiple times, clattering starter but not engaging........

What exactly is the clatter ?? Just a slow spin on the flywheel and then it starts ?? Or a Click click a lot of times very fast ??

Try jumping with another battery and see what is does...... Where is the clicking coming from ??? Under the dash ??

Let know Mon Ami ~!~!

We also need more info on the engine and the mower........