Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Battery is weak link

I have owned this product about 4 months and have had to replace the battery pack for one unit already.The Battery pack lasted about 4 weeks and then it stopped working it would just get very hot but had no charge. Contacted customer service who had me return the batteries at my expense and they sent me new batteries in a previously used envelope (I mention this as it is indicative of an extremely small shoe string operation not a solid company). The new battery worked fine for awhile but now one battery pack is definitely getting hotter than the other so will probably not last and is out of guarantee. I think this is a good idea just not a quality product needs to be re engineered and made by a quality company.