There is no need for even 0.9A, that is just the max setting till it reaches the switchover to trickle charge current which is probably (depends on design) pulsed and closer to 0.01A.
You simply must have a charger that has the trickle feature, and if it does and works properly, you'd also be fine with the charger on a higher current setting as that is only to charge till it switches over to trickle mode.
want to put it on a trickle charger for the winter since it can get a tad cold in Michigan
Possibly it is counter-intuitive since vehicles need their batteries in good condition to start in cold weather, but for longer term storage a battery self discharges less the colder the temperature.
At the same time, the more drained a battery is, the less protection it has against freezing and rupturing the casing and leaking since it's a wet cell design, but I'm talking about ranges like -75F for a fully charged battery vs 20F for a mostly drained.
Once upon a time ago I made a trickle charger for my riding mower. I just grabbed an unregulated 12VDC rated wall wart, (unregulated meaning without a load the voltage floats up to around 15V-16V, and threw some resistors in series till it measured supplying 10mA, or was it 20mA, I forget now.
In retrospect even 10mA-20mA might have been a "little" too high because after a few years I had to top off the water in the battery. Then again it could have instead just been that the engine charging circuit itself caused this electrolytic water loss since the mower had no alternator, charging kept going at a constant rate based on engine RPM even if the battery was full. Well not really constant since it's a VA type circuit that drops current as voltage rises but effectively no end of charge like a regulated alternator would have provided.