Help BATTERY replacement, who does it


folks my note three older batteries are losing their capacity for my note 3. the nexus 6p will likely be my next phone.

when the battery eventually loses capacity, who or what company can change the battery. i have a nexus 4 for travel and i can buy a replacemnt battery on the internet and either bring it to a technician or try to change the battery myself.

i have read that an owner needs to go rouge to change a broken screen.

any info on how to up date the battery? i would really prefer a owner easy battery chabge like with my note 3, but we all have to adapt to the manufacturers want to do with their design changes.