Red Letter
New York City and Chicago require exit signs to have red letters
Sealed Lead Acid (SLA)
SLA batteries are the most reliable and widely used power source. They can recharge much faster than a flooded lead acid battery, and the calcium added to their plates helps reduce water loss. Sealed lead acid batteries can recycle the gases they produce and can prevent damage to the battery when the charge rate is controlled. These batteries must always be kept in upright positions and protected from leakage.
