How to charge the battery from a motorcycle?

Hello! Depends on which battery it is. A universal advice that is suitable, in principle, for all cases - this is the capacity divided by 10, and charge with such a current for 10 hours. That is, for you it is 4/10 = 400 milliamps. On gel batteries, the current that can be charged is usually indicated, and it can be more than the value I quoted. It is signed as initial current, charging current or the like, sometimes indicated as “less than X A” where X is the current in amperes, which means “current is not more than X amperes”.