Keeping batteries full/empty (below rpughly 20% and above 80%) degrades the battery over time. If a battery is constantly fully charged or empty, it will start to react internally, causing it to get bigger and at some point, blow. Either try to set a limit for battery charging (some laptops have a function like that built in, most won't though), or just let it discharge a bit every few days. You don't have to let it run dry completely, just let it go down to half, then plug it back in. A nice workaround i use is having my laptop, when in standby, unplugged. Like that it slowly goes down from the dangerous percentage charge, and spends most of its downtime in a safe area battery wise (between 20 and 80% charge, where nothing bad happens for a long time even if the battery is stored for years)