I was giving my GBA SP a whirl just now; I purchased it used, but never used it much.

I notice that the battery light seemed to flicker considerably: sometimes it would be red, sometimes it would be green, and there seemed to be no consistent pattern. This is after leaving it charging for a good long time; the light stays green if I play it while the adapter is plugged in.

Does this mean the battery is going bad or something? Is this typical of on older GBA SP?