VRLA just means that the electrolyte is soaked in a mat, which makes spillage upon puncture minimal (compared to regular flooded), and the batteries internal reactions 'recycle' themselves, therefore can be sealed. Just don't open the battery unless you have experience, as it will expose it to too much oxygen and create an internal imbalance, and the battery should last a good number of years.
It's not so much that a constant voltage charger is required, it's more so that you make sure you doesn't over charge you battery (apply too high a voltage when charging). Building on what VFR.CBR said, cheaper chargers aren't the best because most people like to fully top off their batteries before putting them into storage. This is a problem because some cheaper chargers are dependent on a heavier load (a more drained battery) to keep their voltage in check. As the battery gets closer to topping off, the charger sees less of a load and its voltage is less 'restricted' which can lead to over charge and permamnet damange if excessive.
This doesn't mean cheaper chargers are bad, I use them all the time (just think of it as a mastercraft torque wrench vs a snap-on one), it just means you shouldn't plug them in and forget..... but ideally unless you pay top dollar, you shouldn't do that with any charger regardless. With any cheapo multimeter (<$10, the error when measuring voltage to 2 decimals is insignificant in real life) make sure the voltage across the terminals while charging doesn't exceed full. On a trickle 2A charge you don't have to check as often as you do on a 5-10A charge (it should say on the batteries face the recommended charge rate in AMPS); most people caution on the side of slower because well, any battery can be charged slowly...you pay more for the batteries that can charge faster.
If your bike has standby accessories that need continous power over the winter (e.g. an alarm that's a pain to re-set. Even a USB charger slowly drains the battery if it's not charging anything), trickle charge your battery everytime you notice the voltage drops too low every few weeks OR buy a storage specific charger (they're fairly small. I assume that's what you have) and leave it connected all winter.
If you don't have accessories that need power, disconnect the battery, wrap the bolt on wire terminals in tape so they don't accidently short to the frame while the other is still connected to the battery (or put a rubber stoppers on them, anything non-conductive), top off the battery (leave it disconnected), and check back in 2-4 months if it needs to be topped off....or whenever you need comforting
Topped off voltage: 14.1 V
Lowest recommended: 12.9 V
Permanenet damage: 11 V
Anywhere within 12.9-14.1 volts and you don't have to do anything, but once it drops below 12.9V, charge it.
If you're worried about your trikle charger, leave it plugged in like you have the past few winters and check that the battery voltage doesn't exceed 14.1V (some batteries can handle 14.5V)
