Cycle count of 1000 is just an expected life. If you run it dead a few times (not accusing, just saying) that will shorten battery life. If you leave it plugged in all of the time and only use it on battery once per month, you can get more time out of it but maybe fewer cycles. Or maybe you just have one of the batteries that was never going to deliver 1000 cycles.
When you can only charge it to 80% of design maximum, the battery is past useful.
Further, old batteries, especially old batteries you continually try to charge, *can* swell, causing misbehavior in keyboard and trackpad, leaking chemicals, deforming the case. Do not delay getting it replaced. For Retina systems, the battery is glued inside a case you are not supposed to even open. For non-Retina, the battery can be replaced by you but you may not want to risk the surgery and let Apple fo it for about $150.
Website http://www.coconut-flavour.com/coconutbattery/ lets you download a program that gives you this kind of display. Mine (below) shows I have more than 100% of designed maximum battery currently. You will note I have few cycles now, and may never reach 1000 cycles but still should get a good life-use from it.
You will note my battery says "FULL" when it is 96.4% full and plugged in, because the charging system will let the battery discharge a little down to 95% as "a little bit of exercise" before charging back to 100%.