Electronics, Lighting, & Gadgets - Building a batterypack

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intrepidbiker
09-10-07, 10:25 AM
The local Meijer's department store here has a 50% sale on Rayovac products. I bought up a Rayovac universal smart charger and 12 NiMh 2500mah AA batteries (they also have 9volt, C & D cell rechargeables at half price. I got the smart charger for $10.50 and the batteries for $9.00. I'm using the AA's in some hokeyspokes (http://www.hokeyspokes.com/) I bought for night commuting.

Seeing that the rechargeables are less than $1 a battery, I'm thinking about replacing my 12 volt, 5ah SLA (which weighs about 4 lbs) with a NiMH battery pack.

My commute runs about 1 hour, although I like the idea of a longer battery life if I should decide to go on a longer night-ride. I use a 9LED taillight which uses about 1.3 watts, a 10 watt low-beam, and a 20 watt high-beam. I do not use the high and low-beams together.

So, how would I go about building a NiMh battery pack for my 12 volt lighting system? If I could make a battery pack that would fit inside a waterbottle, yet later separate the batteries for use in my charger, that would be great (the charger can recharge 9volt, AA,AAA,C, & D cells)

Sir Lunch-a-lot
09-10-07, 12:18 PM
One option is to go to Radio Shack (or The Source, depending what it's called where you are) and get AA battery clips that can hold 8 batteries and work with your typical 9-volt battery connector. That's what I did for my home-brew franken-flashlight.

The thing with NiMH is that they produce 1.2 volts and not 1.5 volts. However, this may not be an issue, because I have heard that most 1.5 volt Alkaline batteries drop to 1.2 volts very early on in their use. If you power supply needs to be exactly 12 volts, then you will need an additional battery pack (although I found that the 9.6 volts 8 batteries produces does nicely for a 12 volt halogen bulb). You may want to get a slightly more expert opinion that mine as far as your voltages go.

The other thing with NiMH is that they lose their charge quickly (self discharge), so they will be mostly dead if they sit around for a month, which isn't a big deal if you are using them daily.

Hope that is of some help