Review on Tenergy 9V NiMH Rechargeable Batteries, 200mAh Long-Lasting Square Battery for Smoke Alarm/Detector (2 Pack) by Jessica Lawson

I have a clock radio that uses a 9 volt battery as a backup during power outages. If the power goes out, the clock display will turn off to save power, but the battery will continue to show the time, and if your alarm is set, it will sound as normal. The watch has a low battery indicator to let you know when you need to replace (or charge in my case) the battery. I used one of the first old 9V NiMH batteries that didn't have low self-discharge and had a capacity of 150mAh. and I think about 7.2V at the output. When it was fully charged and I plugged it into the clock radio, it literally took 3 or 4 seconds for the low battery indicator to come on. Apparently the battery voltage didn't exceed the threshold of the signal light, so it immediately lit up and stayed on. The battery had enough power to start the clock if the power went out, which was good, but it annoyed me that I couldn't know when the battery was dead. Through trial and error I found that the battery would only last about two or three months due to the self-discharge during that time. And all without a power failure. So I went with this new 9V low self discharge battery to see what happens and couldn't be happier. It's a higher voltage, so the low battery indicator is off now (at least not yet). I ordered these along with the Tenergy TN141 2 Bay 9V Smart Charger for NiMH 9V batteries and quickly charged the battery before use. It's been about a month now and I just took a Delkin Devices DD/BATTEST MULTI RoHS AA/AAA battery tester and checked the charge level and it still says full which is great, the old battery should be dead by now. about 50% charge at this point. I will use the battery tester again when the low battery indicator comes on. Depending on the charge level at that time, I may be able to use it for a while after the indicator lights up. Over time my smoke alarms and other devices around the house will fail as will my other 9V alkaline batteries, I will definitely be replacing them with these. There really is no reason to use traditional alkaline batteries in place of these new low self-discharge rechargeable batteries, with a few exceptions where rechargeable batteries are simply not a good option for a particular device. But for most of our devices, this is the way to go and will save us a lot of money over time. Using these batteries will likely save you from having to buy 9V alkaline batteries again, as each can be recharged up to 1,000 times. This is a good chunk of the changes saved here. For each of those new 9 volts you bought you would have saved 1,000 times the cost of the alkaline 9 volts which even if they were only sold at a dollar each would have saved you $1,000! This is absolutely ridiculous. In a ridiculous "I really like it" style! These modern, low self-discharge NiMH rechargeable batteries are another small but useful innovation that makes our lives a lot easier. Highly recommended.*** Update Sunday 10th June 2012 This discussion got me thinking about how long the smoke alarm will give low battery warnings when using low self-discharge NiMH batteries before the battery is fully charged and the Warnings don't stop? I had a Kidde NightHawk smoke/CO2 alarm to test and like many new alarms it runs on AA batteries so I tested a couple of Imedion AA NiMH batteries (three) with low self-discharge. I drained the batteries until they were about 25% full, plugged them in, and then waited a long time before I heard the first low battery warning. The alarm manual states that when using alkaline batteries, the low battery warning lasts at least seven days. Since these batteries drain faster than alkaline batteries at the end of their life, I figured the warning time would definitely be less than seven days, maybe 2 to 5 days. However, what I found was the complete opposite! To my great surprise, I stopped the test myself before the batteries were completely dead. Why? Because the alarm clock gave me constant low battery warnings for the whole three weeks. I really didn't have to see how long they last after that. So it is clear that the undervoltage cutoff point that triggers the warning was high enough that the NiHM LSD battery still had enough voltage to keep the warnings going for some time. long time before it reaches the steep (and fast) point of impact. Maybe a NiHM LSD 9V battery like the Tenergy will last longer than you think, depending on the device you're using. Maybe in the future we'll hear from someone how the 9V battery works, either at Revain or elsewhere.