load test the battery. its not uncommon for laptop batteries to prematurely fail when they're always energized. a faulty battery can cause some odd behavior. the laptop power adapters are another common failure point.

best practice is to routinely exercise the laptop battery by allowing it time to discharge, then recharge. this will help prolong the battery life.

also consider a cheap uninterruptable power supply (UPS) if you're using one as a node.