Yes, LiFePO4 battery can be mounted on their side. However, there are a few things to keep in mind:

1. Ventilation: The emergency ventilation should be free.
2. Heat Dissipation: A battery installed on its side may produce and dissipate heat differently than a battery installed upright.
3. Manufacturer Guidelines: Some manufacturers may specify certain orientations for their batteries.

So, while it’s possible to mount lithium LiFePO4 battery on their side, it’s always best to follow the manufacturer’s guidelines to ensure the safety and longevity of the battery.