4Packs Replacement for Invisible Fence Batteries R21 or R51 Compatible with Invisible Fence for Dogs Fence System

Update: Received reply from company with code to receive replacement batteries. Very satisfied with response and product.Good product for price point. However, one battery pack was dead upon arrival. Sent em to Bsioff and never received a response back.

Our dog’s collar was flashing and needed a new battery asap! Thanks to Amazon Prime and the great value for the four pack, we were able to change the batteries in both our dogs collars within 48 hours (and have back ups on hand when/if needed). Easy to use, fast delivery, and best of all we have the security of knowing our dogs are safe in our yard! Batteries have a great life too—going on month 3 and the batteries are still working great!!

This company should be sued out of business. I bought these batteries for a collar that I was using to train a rescue dog. Normally such batteries should last a year or more. The training was going great, and the dog really respected the boundaries as I walked the perimeter with the dog on the leash. After about six days, the dog would also respect the boundaries off leash, only testing the fence once or twice. On day seven, the batteries died. I was unaware, of course, but the dog walked right through the fence and attacked my neighbor’s dog, injuring it badly. I tested the three other batteries, and they all died within one week. I ordered a replacement, and all four of those batteries died within a week. People rely on these batteries to keep dogs within a perimeter. These shoddy batteries should not be allowed on Amazon and this company should be shut down.

Many have said they had at least one dead battery. I measured the voltage of all the batteries upon receipt and they were all good and nearly identical voltages. Do my experience was good this go around. I'll update my review if I ever get a bad one. My only knock is the plastic casting is just a bit "cheaper" than the name brand, but it's a fraction of the price and these are disposable after a few months anyway.

I read some reviews that some will not last. My last set ordered- a different brand, I had that happen. I’m guessing you get a dud from time to time, but they are way cheaper than the name brand ones….so I’m okay with a bad one every now and then. The collar flashes when they are low so I know and can replace, so I’m ok with that. So far , no issues. Decent product for the money!

These have been working well, but have a tendency to go missing from my dog's Invisible Fence collar. I generally find them eventually in the yard. I finally ran a thin strip of duct tape across the battery and it seems to be holding.

Very easy transaction. Shipped very promptly, delivery just as fast.I was a bit skeptical about buying an off brand, but these are just as good as the well known brand name, but for far less money.To me this is a win!

Received a package of 4 batteries. I needed to use two right away. I opened two and one didn’t work. Needed to use another one. Have not checked the 4th one yet.