The short answer
Almost always, if the phone is otherwise fine and still getting security updates. It typically costs a fraction of a new handset and restores most of the original endurance.
- Check battery health in the phone's settings.
- Check how long it still gets security updates. That, not the hardware, is usually what ends a phone's useful life.
- Get a quote from the manufacturer and from a reputable independent repairer.
- Weigh it against the replacement cost, not against the price of the newest model.
- A phone with a new battery and current software is often indistinguishable in daily use from a new one.
What will ruin it
Very cheap third-party batteries are a real fire risk and frequently report false capacity. Use the manufacturer or a repairer who will tell you what cell they are fitting.
Why it works
Nearly everything people describe as "the phone getting old and slow" is a degraded battery. Phones throttle performance to avoid unexpected shutdowns when the battery can no longer deliver peak current.
Tipking is general household information, not professional advice. Test anything on a hidden patch first. Full disclaimer.
More phones
How to make a phone battery last longerHow to free up phone storage without deleting photosHow to stop a phone being useful to a thiefHow to stop nuisance calls and textsHow to take a better photograph on a phoneAppliance Running Cost CalculatorWhat any appliance costs per use, per week and per year, plus eighteen worked out for you at today's rate.Open the calculator →