iPhone 6s battery will show only 1%, then will jump to 43%

Susanrios wrote:

Apple store replaced the battery. 2 or 3 years ago. Can it do ok with another battery from Apple? Do u know if it’s still $29?

$49 now. The $29 promotion ended in 2018. There are also conditions where Apple won't do a battery replacement. Is your iPhone 6s in good shape?

The format doesn't copy over so well, but this is the part you need.

iPhone Battery Replacement - Official Apple Support

Phone SE (2nd generation), iPhone SE,

iPhone 6s, iPhone 6s Plus,

iPhone 7, iPhone 7 Plus,

iPhone 8, iPhone 8 Plus,

and all other eligible models

Out of warranty

$ 49

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If your iPhone has any damage that impairs the replacement of the battery, such as a cracked screen, that issue will need to be resolved prior to the battery replacement. In some cases, there may be a cost associated with the repair.

Replaced 2 or 3 years ago by whom?

Probably needs a new battery. Even if it's an OEM battery showing decent battery health, there can be weird failures sometimes. You can get a diagnostic to see if any faults were logged.