Hi again Christian.
Unfortunately, I don't have mine with me at the moment so I can't give you the exact range. I am sure you can find this information onlline if you look carefully. Keep in mind that the "audible" range depends on the combination of "stops".
I have noticed that the range is not always exactly the same on all models. If you are talking about squeeze-boxes in general, besides the standard full-size piano-accordion, then you are facing a bazillion different instruments with all sorts of range variations.
You cannot write as if for a piano. Some things to keep in mind:
*The piano-accordion is a portable reed organ
*Only the right hand plays piano-style keys (although double-keyboard models do exist, they are very rare)
*The keys are much smaller than a piano, so you can play larger intervals with ease.
*The number of simultaneous notes that the right hand can play depends. Usually the limit is five (one for each finger) however, since the keys are so small, it is easy to take two adjacent white or black keys with the thumb, or more rarely another finger. Taking both a white AND black key with the thumb is only practical on models with very low black keys.
*The entire right hand can be used for clusters of more than 5 notes. This is a very effective sound on the accordion.
*The action of the keys is considerably faster than the piano, so absurdly fast figures are both practical and idiomatic of accordion style.
*Grace notes are very effective and common.
*Glissandos (using the thumb, middle fingers, etc) are easy and effective.
*Broken octaves or other large intervals are effective. The speed at which these become impratical depends on the skill of the player.
*The bellows control dynamics for BOTH halves simultaneously... for example, you cannot do a crescendo with the piano half while the chord half stays the same.
*The octave stops can be defeated for a very sweet, pure single-reed sound, excellent for soft dynamic levels. The basic model has 3 stops, low, middle and high. Any combination of these can be used. Fancier models have more options.
*Using, say, just the low reed, then the high reed on another passage has the effect of a large pitch range. When all stops are going, our ears hear it as one sound.
*The chord side (left hand) is difficult to conoceptualize unless you have an accordion in your hands. I reccomending picking a used instrument up (make sure all the keys work) for cheap and experimenting with that. There is probably a diagram somewhere with a chart of what each button does. If it seems complicated, keep in mind that the SAME pattern is repeated for each row of buttons, except the pitch is transposed.
*You cannot write just anything you want for the chord side. There is no substitute for having an accordion at hand to determine which changes and simultaneous buttons are possible. Some close leaps that are easy on the piano are tough on the accordion, or impossible.
*Chord substitutions are your best friend when writing for the left side. Sometimes you cannot get to the next chord, but you may be able to change at least the BASS note while sustaining the chord. If anything, you can come up with some very interesting harmonies by just experimenting with the left side. Dissonances and so are are very mild on the chord side, so you can get away with layering these under other instruments playing the "normal" voicing.
*Left-side chords involving just the bass notes are effective, especially drone 5ths.
*Some players (especially those playing in an ensemble.) use only the piano side, or at least use it far more often than the chord side.
*The louder the dynamic, the less notes that can be played on a bellow movement.
*Good players are adept at changing bellow directions so quickly it's barely noticeable (important for loooooong mood drones), but in a sustained crescendo, this break is likely to sound crappy, so keep air limits in mind. Like a brass player, it will run out, but unlike a brass player, it can take a full breath instantly.
*Remember to milk the bellows for all they are worth! The dynamic capabilities of the accordion are it's chief asset.
*The bellow themselves are often used for note attacks. In this technique, the notes remain depressed, while the player jerks the bellows. Another similar effect is to shake the bellows so rapidly that a tremelo results. This tremelo can even crescendo or decresendo to a small extent.
*A series of silence-to-loudest crescendos, at each chord change, that each cut off instantly into silence at the loud point, are very effective.
I hope some of this was helpful.