I don't know about Giant or Specialized. Generally speaking, if the case can be disassembled (screws or seams that can be cut) there is a good possibility it can be rebuilt. Some batteries have molded cases which can be very difficult to take apart.
A few places to check are:
www.hicbattery.com
Among others, this place lists Giant rebuilds:
Call ebikemarketplace to get a quote for any ebike Battery Rebuild 888-456-9410 How to Replace an Electric Bike Battery if the Model is Discontinued
ebikemarketplace.com
This site says they will rebuild ANY e-bike battery:
How to Replace an Electric Bike Battery if the Model is Discontinued or the Company is Out of Business?
ebikemarketplace.com
>> Reention Batteries >>Shan Shan Batteries >>LOVA Batteries >> Dorado Style >> Hailong Style >> Silver Fish Style >>Reconditioned Batteries "2 Years Parts & Labor Warranty on all Brand New FTHPower batteries"
www.fthpower.com
There are various you tube videos on how to do it yourself but it requires a good deal of skill. There is also a certain amount of risk involved should you make a mistake.