Battery won't stay charge

I have changed stater magneto check all wires why do my batteries die

With engine started and running WOT what voltage do you get at battery?

Your batteries die because you are either not charging them or you have a parrasitic load on them.
With a fully charged battery, mow your lawn then disconnct the - battery lead
If the problem goes away there is a short somewhere.
If it makes no difference then there is a charging problem.
On some mowers the recharging power has to go back through the ignition switch and over time this burns out.