If the battery drains down after a few days, something is wrong.
Same if after a couple of weeks.
Save your money, get one of those portable lithium batteries that you can take with you, best bet.
Don't run around lugging the engine or let it sit with ignition on not running.
Check it once in a while or install a VM so you can see ow it's doing. If you let it sit for a longer time and see it needs a jolt, give it a charge using a high quality bike charger but don't let it sit in a trickle charger.