To revisit this topic, RM 2K is out of warranty exchange for a (refurbished) unit. However, due to the low number of iPad Pro devices, you will probably end up with a new unit.

In warranty repair requires the Apple Authorized Service Provider to run some battery test, which might not show any problem if it is still running but with degraded usage time. In that case the RM 2K fee will still apply if you insist on replacing it. The only time device replacement is done at a lower cost is due to bulging batteries.

It is not worth it in my opinion since a new iPad 8 gen is faster than the iPad Pro 9.7”, except foe the pro-motion screen and quad speakers.

Ended up getting the battery serviced at a third party repair shop. But somehow iPad Pro battery replacement isn’t really available. One shop outright refused to do the replacement. The other shop i tried did something for RM 200, the unit which was not powering on when I sent it in is working again but the battery life still sucked and drains to zero within one day just idling. 

Bought a new iPad 8 gen as a replacement and the old iPad Pro is used as a HomeKit configuration terminal now.