Question - Can I install this under the bonnet in a car engine bay?
Response - As for installing the battery under the bonnet, the main concern is heat. Our batteries are designed to operate up to 60 degrees C. This would be sufficient under most conditions, however there may be situations where the ambient temperature gets very hot such as in hot summer conditions and when the engine is working particularly hard, where the temperatures under the bonnet could cause the battery temperature to exceed these tolerances.
Our battery management system does contain a thermal valve that would disconnect the battery should it overheat to protect the battery from excessive damage, therefore this is not a safety hazard. However, regular exposure to excessive heat can significantly reduce the battery life.
Therefore there is no simple answer to this. It would depend significantly on where the second battery tray would be located in your engine bay (i.e. it would make a significant difference if it was close to the front near the radiator with good airflow, vs. tucked away next to the turbo charger), and the conditions that you would run your vehicle under.
Consequently, as a basic rule-of-thumb we do not recommend it. However, we do have several customers who have installed our batteries in the engine bay but they understand the potential impact. If there is evidence that the battery has been operated under excessively hot conditions, then that may affect the warranty.