Battery pretty suddenly stopped holding a charge for more than an hour, and charged very slowly.
Two screws were stripped before I started, and I couldn't get them to budge. Luckily, the cover is flexible enough that I could bend it up enough to get at the battery. It was awkward, but doable. Also, the battery was very firmly attached. Using 90% ethanol was effective (and necessary). The repair was ultimately successful, and effective.
Be careful with those screws; it isn't hard to strip them. And have some ethanol handy.