Q Although its condition is still reported as being normal, the battery in my MacBook has swollen. Would one of the much cheaper replacements be a wise purchase, given that I invariably use the MacBook on mains power?
A Profit margins on replacement items like batteries can be very high, and you may find that a bargain basement battery comes from the same factory and production line as the full-priced original.
However the penalties of battery failure can be very serious, and there have been enough problems with full-price branded batteries. Overheating batteries only very seldom cause fires, but when they do the consequences are disastrous.
Whether you decide to run that risk, you must care for your battery to keep it in good condition. Every couple of months, disconnect your MacBook from the mains, use it until it starts showing low battery warnings, keep using it for longer still, then recharge it fully. That will not prevent battery problems, but should stave them off as long as possible. Always using a laptop on the mains, on charge, tends to shorten its battery’s working life and can in some cases lead to swelling or other problems.
Updated from the original, which was first published in MacUser volume 28 issue 25, 2012.