I have two Motion Minis. One I use and a new one still in the packet as a spare. ( sorry , not for sale ) .
My question is , with the new one , should I use it every now and then and drain the battery some ,then charge it , or just top the battery up every few months. Trying to keep the battery in top nic. I may not need it for years.

All batteries - lithium included - will have some self-discharge. This is an artefact of chemistry and of construction. We do see come batteries marketed as "long life" - their self-discharge will be small, lasting 10yrs or more. All rechargable batteries are considered to be *not* long life - lithium cells are quoted asa 1% per month / 10% per year. Importantly, if a lithium discharges below a certain threshold - 2v per cell - then they are considered to be unsafe to be recharged.

Thus a typical suggestion is to charge them at least once per year or two.

Some manufactures stipulate more often - for example, DJI drone batteries have a self-regulation mechanism which discharges sooner, so need to be charged about once per 6 months.

Note - new gadgets dont often come with full-charge in their batteries. This is primarily for safety reasons, because charged battery can let out the magic if it gets bumped a bit hard. And during the manufacture of the battery it wont get charged up completely, and the manufacturer of the gadget also wont charge the battery. So you will want to do it sooner, rather than later.