The flickering is a sign of insufficient voltage. Either the battery is marginal, or the power regulator board has a problem.

The crashing could also be due to power instability. If, for example, the regulator is a bit loosey-goosey, then the voltage could dip too much on a transient basis, causing all manner of mischief.

If the flickering and unstable behavior both appeared at the same time, then a common cause -- e.g., power board anomalies -- is made more likely.