Don't use a trickle charger on a starter battery.
Trickle chargers are made for storage / deep cycle batteries as used in camper vans, boats, UPS, alarm systems etc.
Trickle charging a starter battery will cause sulfation and premature failure.
Best to get an AGM battery which will not require any maintenance charging for months due to its extremely low self discharge rate.
If you want / have to use a flooded cell battery (which is a kark idea in a dirt bike which gets dropped occasionally) use an ordinary maintenance / workshop charger and charge the battery once every month until the charging current drops to near zero. If you're lazy get an automatic "intelligent" maintenance charger which cyclically recharges the battery.
Don't get an intelligent charger for an AGM since you are wasting your money.
The trickle charger i've got specifies that it's for motorbikes batteries, 0.2 amp charging (don't know if that's per hour or minute). It charges till 13.5V potential difference is measured across battery terminals, then it discharges it to 13V, and starts again to charge to 13.5V etc. How is this bad for the battery? How would this cause sulfonation?
It does not cause sulfation like continuous trickle charge does in starter batteries.
But it causes the plates to distort like normal operation of the battery would.
Using an "intelligent" maintenance charger on a flooded cell battery is just like cycling the battery on a daily basis. The charger is therefore best referred to as a charging cycle charger. There isn't anything intelligent about them.
From a wear point of view it's like cranking your engine for a minute or so and then starting the engine & recharging the battery.
The AGM basically goes dormant and thanks to its very low self discharge you don't need to do anything to it even if it stands for a month or three.
This makes an AGM starter battery way superior in all applications where the battery is used intermittendly. Bikes, jet ski etc.
No leakage if tipped over or inverted, a generally longer service life if compared to flodded cell and the fact that they pack more punch for a given capacity (both "cranking power" and useable capacity) are other advantages.