0frollardBest Answer 9 years ago ReplyUpvoteDepends on the cells - 4 amps into a 3Ah battery means it would charge in 3/4 hours (45 mins). Quick chargers like this are common, but they reduce the useful life of the battery. (in charge cycles before failure) Safe? probably. BEST for the battery? not so much. A slower charge will be better for the battery. Applying 1 amp would take 3 hours to charge the battery, and extend its life "an amount I can't guess". Lastly, the battery probably gets warm during charging. If it gets hot, you're cooking it with too much current or overcharging it.