Now it is not that bad.The engine will start missing and breaking up at full throttle.Like someone said sounds like it is going rich on carb.If and when this happens throttle back and head for a landing ASAP if you have to make a go around do not go to full throttle,sometimes battery will recover enough t o make a safe goaround. Do not try this unless you have to. Keep check on your ignition battery and do not every use a battery that you would not trust on your radio.
BCCHI