You don't have to get the charger. I didn't get one with mine.
The charger allows cell balancing to evenly distribute the charge.
I've seen some chargers for lithium batteries where one can see the charge distribution across all the cells. My buddy has one of his battery.
These batteries can be put on a shelf and left there for quite a long time with hardly any charge degradation.
I've had a Shorai LFX18A1-BS12 for my RC51 sitting on a shelf in a box since March 2012.
In that two year period, it has lost .02V. It arrive at 13.34V, and is now at 13.32V.
So a charger really isn't needed usually.
For bikes that have a power take-off such as a clock, then maybe a short top up charge, or just crank up the engine for a short time.
These batteries charge quickly too.
The important take away is this, they use different chemistry than a lead-acid battery, and therefore have different ways to treat them.
If the battery goes into a low charge condition (down to 12V), recharge it as soon as possible.
And if the battery goes into a dead state (11V) be sure and charge ASAP!
And do NOT fully discharge the battery (0V). Once that occurs, the chemical structure is permanently damaged and won't recover.
It's all on Shorai's web site.