Your question is not well phrased. Is your battery never fully charged, or can it be charged but doesn't have enough time? If it is the first case, it is recommended to check whether the battery is short of water or there is a short circuit battery, and if it is the second case, it is completely OK.
Bad for the battery. Battery life is short.
But you can, but try not to do it, because it will hurt the battery and shorten the life of the battery.
First eliminate the charger problem, lead-acid battery is easy to have virtual electricity, looking at the battery is full, use up quickly, you try to put the battery deep discharge several times, repeated charging several times has no improvement. If you didn't change the battery!!