I do a lot of woodturning, so eventually it was necessary for me to buy an air supplied shield. After hours of research I decided the Trend Airshield Pro was the best choice for me. It was expensive, but with some more research I found one online for less than $300. It works great. I'm really happy with it. After about a year the battery refused to hold a charge. No big deal--rechargeable batteries wear out, won't hold a charge and need to replaced occasionally. I went online to buy a new battery and was shocked at the price. They cost $70. I thought that was crazy. I took the battery out of the helmet and noticed that it was just a plastic container holding a battery pack. The battery pack is marked 3.6 volts, 3600 mah. I took the plastic container apart, which was really easy. It just snaps together. Inside was an unlabeled, shrink wrapped group of three batteries. I scoured the internet looking for a replacement but could find nothing. You can't buy a 3.6 volt, 3600 mah battery pack. It looks like Trend had this battery specially manufactured just for them, forcing you to pay three times what the battery should cost to keep your AirShield Pro running once the battery wore out. Things like this really piss me off. I have no problem with companies making money, but when they design products that require purchasers to continually pay for that product by forcing their customers to buy overpriced, proprietary consumables, I refuse to play that game. Had I known I would only get a year out of a $70 battery, I could only buy from Trend, I would have bought something else. I decided to try to make my own battery. Below are photos and step-by-step instructions so you can make one for yourself. It is very easy to do. I am not very handy with electronics, but I have some basic soldering skills and that is about all you will need to make your own battery. Click the photos for a larger view. Before you begin, take responsibility for your actions. I'm not an electronics expert, and can't guarantee you won't hurt or kill yourself. This may be dangerous if you don't do things correctly. You could fry your helmet fan if you connect the batteries incorrectly. It worked fine for me. Proceed at your own risk. Here is what the battery looks like after it is removed from the helmet. Now, carefully pull the two halves of the battery cover apart. The batteries are glued to the bottom cover. The glue is like rubber cement so you can just pull them from the bottom cover. This is the view of the bottom of the batteries. Here is the top of the batteries. Remove the red protective covers. They are just paper glued on to cover the connectors. Cut all the wires from the old batteries at the terminals. Leave the wires connected to the battery cover. Here are the replacement batteries you will have to buy. I did some research and the best deal I could find was from batteryjunction.com. Order 3 Powerizer-4-3A-NIMH-3800wTa. They cost $4.24 each. With shipping and tax the total was $18.24. If, for some reason, you want to buy batteries at some other place be sure to get 4/3A NiMH batteries, at least 3600 mAh (I got 3800 mAh because that is what Battery Junction had. mAh stands for milliamperes/hour. You may also find it listed as 3.6 Ah, same thing.), flat top with tabs. The tabs make it easier to solder them together. These batteries are 1.2 volts each. Three connected in series creates a 3.6 volt battery pack. These batteries came with a piece of heat shrink tubing on each of the positive terminals. Pull them off. I used a clamp to hold two batteries together while I soldered the tabs together. The battery on the right has the positive terminal, or the end with the white ring, facing you, and the battery on the left (which will be the center battery) with the negative terminal facing you. I folded the tabs over each other and soldered them together. I flipped the batteries over so the terminals are opposite of the above photo. I soldered the red wire that is attached to the battery cover to the tab on the positive terminal of the right battery. If you look in the upper left corner you can see that I soldered the black wire attached to the battery cover to the negative end of the third battery. With a few dabs of hot glue, I permanently connected the three batteries together. Also notice that I soldered the white thing with two wires to the remaining tabs. I don't know if this a resistor or what, or if it is even necessary, but I thought it would be a good idea to use it. If you look carefully you will see that I folded the long tabs closer to the batteries and covered them with hot glue. I figured this would both insulate the wires and stabilize them in case the solder joint failed. Not the neatest job, but this was an experiment and I wasn't going to get carried away until I'm sure this would work. Stuffing the batteries back into the battery cover. I didn't glue the batteries to the cover like the manufacturer did. Once the top cover is snapped on they aren't going anywhere. The battery reassembled. Testing the output with a volt meter. Batteries came charged and ready to go. I put the battery back in the helmet and the fan worked perfectly. Total time to replace the batteries was about a half hour. Cost was less than $20. Definitely worth the effort. It was also rewarding to get around Trend's trap of overcharging for their replacement batteries. I'm sure Trend pays only $5 or $10 for these batteries. It's ridiculous that they sell them $70.