Unless you wanna be like Edison Chen, I rather backup myself and do a hard reset before sending for battery replacement.
Huawei Singapore customer service is good in my opinion, they go beyond their required job scope and make customer oriented recommendations.
I remember I cracked my front screen during the 1st 90 days of purchase and send it to huawei west gate svc centre for repair.
The serving staff asked if I wanted to replace the battery foc since I was already sending it for repair. If she didn't ask, I wouldn't know I can get foc battery replacements within the warranty period.
Only need to pay for svc charge which wasn't alot (I can't remember how much) and I've made it a point to do battery replacement during their cust svc day (svc charge is foc for certain phone models iirc).
And even though they quote me 2-3 days for phone to be returned to me, I usually get it back on the same day.
Probably because no one buys/uses huawei lol
Anyway, even if warranty is over, just do replacement via their support app found in your phone.
The online staff support will advise you the process and pricing accordingly.
If there's one thing that I really liked about huawei, it's their after sales svc support.
Its such a pity I can't use gms on it, otherwise I would have long gotten P40 Pro+.
+1 EDMWER app