Starting the engine (cranking amps) is only one part of what the batteries does. Your battery is also part of the charging system and the current from the alternator recharges the battery when the engine is running. You must use a lithium battery that is designed to handle the MAX current from the alternator, otherwise it will cause premature failure.  For our batterie the maximum charge current rate is 5 x amp-hour. As an example, the ETX900 is a 16Ah battery so the max charge rate then is 80A (5 x 16 = 80Amps).