VRLA Lead-acid  batteries have long been the UPS power system source preferred by data centre operators, due to the reliability if well-managed & low initial project cost. However, li-ion batteries has been capturing more interest for some time now. 

Lead-acid battery (VRLA) is a battery whose electrodes are mainly made of lead and its oxides, and the electrolyte is a sulfuric acid solution. VRLA Battery 200% Heavy then Lion battery.  

Lithium battery is a kind of battery that uses lithium metal or lithium alloy as negative electrode material and uses non-aqueous electrolyte solution. Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries.

Usually VRLA battey use at 50-80% Deepth, and Lithium battery use at 80-100%. 

Lithium Battery is light weight, but May explode if used incorrectly!  VRLA Battery is a little heavy, but its 100% stable and safe, will never cause danger to you!

Btw, Lead in batteries can  be recycled and reused, reducing environmental pollution. Lithium batteries are not recyclable, they can only be thrown away when worn out.