Perimeter Technologies Four Pack Dog Fence Batteries for Invisible Fence R21 or R51 Receiver Collars (4-Pack)

These cap batteries have become a staple in our home. We have multiple dogs on our Invisible Fence and their propriety batteries are far too expensive for their short life so I went looking for an alternative. Reasonably priced with markedly greater durability, these batteries are the answer! They are always delivered quickly and well packaged. Will continue to repurchase as needed.

Great product. Works very well!

Works as well as the invisible fence brand.

Bought four of these batteries for our Invisible Fence brand collar, P/N 900-0025-02. As far as I know, these batteries are supposed to be compatible with this collar; perhaps the seller can let me know that's incorrect. I followed the directions on the package: remove old battery cap, wait at least five minutes, insert new battery cap, wait at least 10 seconds before testing. Upon initial insertion of the new, Perimeter-brand battery cap, the green LED on the collar blinks green several times, as expected, and the collar functions as expected – it beeps, and presumably provides a shock, when moved over the fence line. However, a couple of hours later – nothing, no beep and no shock. The only reason I checked whether the collar was functioning properly was because a couple of days after inserting the first of these battery caps, I noticed the collar's LED blinking red, which usually means the battery is low.I went through the process several times of removing the battery cap, waiting, inserting, verifying correct operation immediately after inserting the cap, and then finding it inoperative just a few hours later. I found the same behavior with three of the four batteries, both when I initially removed them from their packages, and re-testing them several times over the course of a few days. I ran out of patience and interest and have not opened the fourth.I put a meter on each of the batteries I tested and found the voltage to be the same as that of Invisible Fence brand batteries. The current was over 1,000 mA, which is the upper limit of the meter I used. I didn't have a brand new IF brand cap to measure, but for the sake of comparison, an Invisible Fence cap that we removed because the collar's LED was blinking red, showed between 600 and 700 mA.I noticed a physical difference between these caps and IF brand caps. On IF brand caps, the surface of the negative contact of the battery, which is the inner circle of exposed metal on the business end of the cap, is flat and it's pressing firmly against the underside of the circular lip that holds it in place. That is, it does not receded when I push on it with, say, the tip of a ball-point pen. On these Perimeter brand caps, there appears to be a creased piece of metal under the retaining lip. The crease in this piece forms a diameter across the inside. This piece of metal is loose – you can feel and hear it move around a little when you shake the cap. I'm wondering if the contact between this conductor and the negative contact of the actual battery, on which it presumably rests, is intermittent, as the dog moves around. If so, perhaps the collar senses the loss of power, shutting itself during the milliseconds while the power is draining. If one is supposed to wait five minutes before inserting a new battery cap because the collar's capacitors have to drain completely before it will properly "boot up" again when power is re-applied, perhaps the jostling of the collar continually makes and breaks the circuit quickly enough that the collar won't start to operate correctly again until the contact is broken for the span of the five minutes. Just a theory that fits the observations; I have no idea of its accuracy.I also wonder why the height of the battery inside these Perimeter-brand caps appears to be less than that of the batteries in the IF-brand caps, necessitating the use of the creased, metal conductor. I've disassembled IF-brand caps (but never a Perimeter-brand cap) in the past and found that the full interior height of the caps occupied by standard batteries. Is the battery in the Perimeter-brand cap shorter? Does this mean that it contains less potential chemical energy to convert into electricity, i.e., will it not last as long, even if it functioned properly?I wrote and submitted this review before contacting the seller in an effort to save others from the same frustration. If the seller responds and somehow rectifies the situation, I will certainly submit an update.

sometimes you have to fiddle with the contact tabs to get them to work properly, but other than that they work fine

Much cheaper than buying from local invisible fence dealer.

Works great! We have to wiggle the ends to get them to make the connection. Just a fyi

Just what we needed