9V2A to 7.4V charging is this is absolutely not possible, lithium battery charging is very strict, charging voltage, current, have to use a special charger to achieve, you can use some chips or circuits to reduce to 8.4v, but it is best not to series parallel charging, if the parameters are different, it is easy to cause the battery to break down, and may explode, it is best to charge alone, Not the original charger, after all.