At least one person has failed to make the bigger battery DIY-way destroying the battery, so it is not so easy for everyone. us$100 is not so much when you doesn't have to tress out being afraid of the fireball in the future, if you are not sure what you are doing.

I have made two of these batteries with two different methods. The first one really I couldn't recommend to average joe. The second easier hack is more doable for everyone, but still if one do not want to worry and has the money, go buy an original Mugen battery.