“Service Recommended” means the battery holds less charge than when new or is not functioning normally. The message alone does not make the MacBook unsafe: Apple says you can continue using it. Swelling, unusual heat or a distorted case are separate reasons to stop.
Decide from the symptoms
If the only change is shorter battery life, arrange replacement when the runtime no longer meets your needs. Unexpected shutdowns or abrupt changes in the percentage deserve assessment because they make the laptop unreliable away from power.
Check Battery settings and note the model and symptoms. A cycle count is useful context, not a diagnosis on its own; the expected cycle limit varies by model.
Stop if the case changes shape
If the trackpad or bottom cover lifts, the seams separate, or the battery area develops unusual heat or a chemical smell, stop using and charging the MacBook. Do not compress the case or try to puncture the battery. See our swollen battery guidance.
What replacement will and will not fix
A replacement can address a worn battery. It will not repair a faulty charger, port or charging circuit. If charging itself is the problem, start with the charging checks rather than choosing a battery from the warning alone.
For a MacBook battery assessment or replacement, send the model and describe the runtime or shutdown problem. Back up a working Mac before bringing it in.