This is a picture of a 12 volt 14 amp hour lithium battery cracked while in use. This battery was designed for use in motorcycles as a direct replacement for the stock lead acid battery. If you Google “cracked lithium battery”, you will find over 450,000 search results at the time of this writing.
Yes, lithium batteries are much lighter, they have a higher energy density, and a longer life on paper than lead acid batteries. Other than being 2 to 10 times more expensive than comparable (by amp hour) lead acid batteries currently are, they are superior in every way, except for the battery management system.
The battery management system is the software/hardware usually installed within the lithium battery case that is supposed to automatically handle everything from preventing overcharging to general battery maintenance and temperature regulation. By installing the battery management system within the battery case itself, the lithium batteries are sold as a “direct replacement” for lead acid batteries. The build quality of the lithium battery and its corresponding management system are probably the most important factors when purchasing a lithium battery outside of its cost.
If the battery management system fails, the battery will too. When a lithium battery fails, it may fail catastrophically. This risk is usually not acceptable for a device designed to protect sensitive equipment like an uninterruptible power supply (UPS). Until the technology on lithium battery management systems is improved as well as standardized and the costs come down significantly, we may not see lithium batteries in most uninterruptible power supplies anytime soon.