Trend Airshield Pro: Build Your Own Battery

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 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.

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7 years ago

Why not have a battery pak that hangs to your belt and a cable that is easy to connect and disconnect?? It would make the unit on my head lighter. I’m not familiar with the electronics, but a question that popped in my head.

John Gerhardt
2 years ago

Great Great Article.. i asked myself the same question and found your fix… Way to Go… just ordered 6 batteries for my trend battery..Thank you so much for posting this… Cheers

Scott Voth
1 year ago

I decided to get back into turning and my Airpro helmet would not take a charge. Like you I was shocked to see what they want for the replacement batteries. I have a spare pack that has never been charged but it is pretty old too so it probably won’t charge up either. I’ll be ordering up the replacement cells today. Thanks for working this out. The price of replacement batteries is a scam.

Scott Voth
1 year ago

I did two packs up following your instructions and everything went well with the exception that the shield would not power up when I first put the pack in. I plugged in the charger and it fired right up and worked fine after that with no beeping. The second pack worked with no problems at all. The white thing with two wires coming out of it is a thermal switch that will open if the pack gets too hot. I’m not sure if this is a one time use thing or if it closes the circuit when the pack cools down. There is also a fuse link between batteries one and two (the link is white and has a little piece of heat resistent material under it). This is impossible to salvage so it didn’t make it into the refurbished packs. We’re only dealing with 3.6 volts so I really don’t see the need for all the extra safety items. If they were lithiums yes but not NiMH batteries. The only problem I see in the future is the replacement batteries are getting hard to find. These were the only 4/3 batteries the place carried. We may have to go with lithium 3.6 volt batteries in the future and you will have to use a different charging scheme with these as that wall charger won’t be safe. You could also go with AA NIMHs and just have to charge them more often.

9 months ago

Man, like the first step with the new batteries didn’t work for me. Touching the positive and negative ends together to solder them produced a spark, fire, smoke. I followed your instructions, I don’t know what I did wrong.