I'm going to be traveling and have a small device that needs to run 3 hours on a 9v battery everyday. I'm looking for a good/great rechargeable 9v battery. I'll have to get 2 of them so I will be able to use one while the other one is in the charger. Does anyone have any recomendations?
NiMH batteries come in 9V size. Some of the AA NiMH chargers even have additional connections for 9V. Should be available at any of the big chain stores that sell NiMH in the USA (if that's where you are).
FYI, my 3-year-old Energizer 9V NiMH's are rated for 150 mA-hr. There are probably better ones available these days.
I have no idea what you are trying to operate or how portable it must be, but if possible, you may want to consider using 6 AA NiMH batteries and commonly available AA chargers. Radio Shack has 6-AA battery holders and the connection is compatible with the 9V plug.
Of course, portability goes to hell with this setup. cv
All "9V" re-chargeables are 7.2V, whether NiCd or NiMh, so take that into acount, that is to ask "does the item run with the NiCd "9V" battery?" Now you could rig up seven NiCD "D" cells in series for 8.75V or eight for 10V and regulate down to 9V. Having larger cells gives a longer useage time after charging.
I have purchased several types off the web, here's what I have found: You can get a charger that charges 2-4 9 volt batteries at a time. They are in a 9volt package, but are a little less than 9 volts. They don't last nearly as long as alkaline, and MUCH less than 9 volt Lithium batteries.
I was using mine for 9 volt LED lighting. I bought a bunch of these Pak-lite flashlights from 9voltlight.com. Even though they seem to last forever, I like the idea of using rechargables.
I found that they are just a little dimmer with the rechargable batteries, and since I use about a dozen of them throughout the house per night (the power goes off often!) I don't worry at all how long I run them on high.