12V 345 Amp lawn mower battery to a 12V 10 amp motor?
The current (in Amps) is determined by the scissor jack.  As long as you provide it with the correct voltage (12V), it will only take the current that it needs.

This is similar to how you can plug in a small light bulb into the same socket that could power an power-hungry hair dryer.  The current flow is determined by the properties of the load.

Here is a good (much more detailed) explanation of how this works.