I bought the CTEK XS 800 Battery Charger which cost about $90. (Try ebay for cheaper again, but wouldn't be too confident on the warranty) There were cheaper options but CTEK was recommended and comes with a 5 year warranty.
If you were purely charging a flat battery the Ctek website recommends higher end models. I believe the XS 800 is more suited to charging smaller batteries, vespas, motorbike jet skis etc... From a maintenance perspective it appears to be ideal.
Will need to use it for awhile before I can give my own opinion on that though…
It has a Maintenance “pulse" function. Below is from the manual / web. Cheers Ash

Four step, fully automatic switch mode model.
Charges lead-acid batteries (Wet, MF, GEL and AGM) from 1.2Ah to 32Ah, 1.2-100Ah maintenance charging.
Maintenance pulse charging increases battery life and gives superb performance.
Charges even drained batteries.
Pulse recover of slightly sulphated batteries.
Low back current drain, low ripple and input voltage independent (170-260V).
High efficiency: 85%
Delivered with two interchangeable connection leads, one with clamps, and one with eyelet terminals.
The charger can be connected for months, ideal for seasonal vehicles.
Compact design with mounting holes for permanent assembly.
5 year warranty.
The XS 800 has a fully automatic, four step charge:
Desulphation
Runs a complete charge cycle within a fraction of a second. The cycle repeats during the whole desulphation phase. Every cycle recovers some lead sulphate into useful material.
Bulk
Charging where 80% of the energy is returned. The charger delivers a constant current until the battery voltage has reached the set level.
Absorption
Final part of the charge up to 100%. The battery voltage is kept constant at the set level, during which time the current drops gradually.
Pulse
Maintenance charging. The state of charge varies between 95% and 100%. A pulse is sent out to the battery if the voltage drops. This keeps the battery in trim when not in use. The charger can be connected for months at a time.
Using the XS 800 gives your battery an optimum service life and operational reliability.