Although your watch is solar-power all Eco-Drive watches contain a rechargeable battery known as a capacitor. They last longer than a regular battery but are difficult to get replaced because nobody carries them. Firstly I assure you whoever opened the watch did damage it. The solar sell is under the dial so removing the back would not have exposed it to anything. Rechargeable batteries do not hold a charge forever and do need to be replaced every 5-10 years. In order to know which capacitor you need you need to find out what movement model is in the watch (this is different than the model number of the watch you must physically look at the movement) (unlike batteries capacitors all have the same number on the cell so you need to know the movement number to order the proper size). Once you have obtained the capacitor repairing your watch because no more difficult then changing a battery. I'd ask those people to take the back off again so you can find out what movement is in the watch. Typically it's a 4 digit number but sometimes it also has letters in front of it and I've also seen them with only 3 digits. If you could supply me with the movement number I can supply you with a the proper capacitor at a price of $45 with free shipping and tracking.