Our batteries are not designed to handle the large amp draw that engines require when starting up.
In general, no you can NOT use our batteries to start an engine on a vehicle or boat.
However, small engines with smaller Amp requirements may work if you connect multiple LiFePO4 batteries together. For instance, the small RV generators could possibly be started if you have 3 or more of our 12V 100 Ah batteries connected together. This is an advanced use of our battery, and you should always contact an electrical expert for advice before attempting to do something like this.