with only 3 AAA batteries, the device is operated (supplied), but has a really strong output, so you can operate extremely intense training also.
Too much or too strong training leads to muscle soreness, as with regular sit-ups, so I recommend to start small.
Otherwise, nothing needs to be replaced except the batteries. After a while you feel the training even as pleasant and relaxing.
I can only recommend the device, can not understand the negative reviews. In addition: If you do not like, you can return them within 14 days, it yes.
