Lead acid batteries do build
Lead acid batteries do build up pressure, but they have vents. So long as the Battery is:
A: Not upside down for charging (The pressure will push the fluids out of the vents)
B: Charge voltage is around 13.8V
You can safely charge a SLA battery and not have to worry about overcharging or damaging the battery. They are truly dumb-chemistry batteries. I charge them using a 12V power supply all the time.