Depends on what phone you have, but most people already saying there's no problems with the battery stock, can get replacement done in the same day.

Ya, should be no problem getting a replacement battery now.

I think all authorized service shops should be able to do a good job on your phone. Since there's also no ingress protection on the 6S, you have less to worry about

need to unlock your phone.

I sent my 6Plus to do battery replacement. They said that my battery is fine even though I have around 1400 charge cycle. And if the batter doesn't last whole day, it is likely to be bloated. So, they went ahead and take a look and then came back to confirm that it is bloated. Bloated battery they cannot replace the battery and so, they want to send to Apple for a 1-1 phone replacement for RM$239 (forgot exact amount). They passed the phone back for me to think if I want to do a 1-1 exchange. My phone was fine.. and I worry if I exchanged to a refurb one there will be NEW problems in the future. Sometimes, I feel these guys are just lazy! They rather not spend 3 hours to fix and suggest a replacement !

Apple websitr down?

Wanna make appointment for battery replacement but fail to load

Well assuming it is a new phone la lol. But from what i've read, Apple's refurbished sets are usually better than newer units since they go through more stringent tests and most of the internals are new.
lol sadly my old model is only a rose gold 16gb.
But weirdly the invoice he typed in the model as grey 64gb 
Hopefully they replace the phone according to his error 

Anywhere between 2-4 hours if you have an appointment.
31 Dec 2018

MACHINES@THECURVE..just collect back my 'new' iphone this morning..went there on tuesday..so far im happy with it..btw my unit manufactured last year so not bad at all..and for refurbished unit they give 3 months full warranty not just the battery

Well assuming it is a new phone la lol. But from what i've read, Apple's refurbished sets are usually better than newer units since they go through more stringent tests and most of the internals are new.
lol sadly my old model is only a rose gold 16gb.
But weirdly the invoice he typed in the model as grey 64gb 
Hopefully they replace the phone according to his error 

Wow that’s fast. Curve Machine fked up my order. I think the staff typed in the wrong serial number that’s why the wrong model was written in the invoice as 64gb grey instead of 16gb rose gold.
2 weeks later and still no movement to my order. Had to call a Apple then contact Machines before something happens.
Btw Machines service center has really shit contact service. Their phone line is automated to reject your calls and the only way you can contact them for info is through their FB messenger page.
Curve Machines.

No they messed up my order. Now they only initiated the service.