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 65 degrees C. This would be ok 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.
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 behind the motor at the back), and the conditions that you would run your vehicle under.
Our battery management system does contain a thermal valve that would disconnect the battery should it overheat to protect the battery from excessive damage. However, if the battery is running hot much of its life, it would shorten the battery life.
Therefore, as a basic rule-of-thumb we do not recommend it. However, we do have several customers who do install 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.