Depends on which area lor
Some place Poslaju and Some place Citylink and Some place ABX.
But always say no to Skynet and Kangaroo.
Kangaroo once did not deliver my parcel, thn when i go to their office to collect, they also dont know where they put my things.
End up i need to find together with them, lastly only find it that they put my parcel with those different delivery area's parcel.

If Document, Citylink, Gdex or ABX will be cheaper as these courier service will charge according to parcel or document.
If parcel within 0.5KG, Poslaju will be cheaper as Poslaju charge RM5.95 for first 0.5kg regardless parcel or document.

Power bank is definitely a parcel.
Use Poslaju then.

Yup, the best is use a box.
Or else you may use a Poslaju Flyer but less secure and most poslaju branch won't provide it unless you have an account with them.

Uhm, depends on the weight of box actually.
coz normally poslaju measure the weight but not the volumetric.
Therefore if the box is light, it will not cost you too much.
You might refer to this link.
http://www.poslaju.com.my/services.aspx#section9

UHm, i can't guarantee but should be ok.
coz powerbank will not broken easily btw and bubble wrap will absorb the force if poslaju accidently drop it.
bot ofcoz Box will be safer

Yup, have insurance.
But if you want to cut cost on postage, insurance is actually a waste unless you post a phone or valuable item.
Insurance will also cost you some bucks.

You must have an physical office.
The benefits are poslaju will provide free pick up service at your office and postpaid payment and also poslaju will provide you with free flyer.