Replacing 7.2-V D Batteries

Should be quite safe to go to one 14.4V battery. Your equipment may well work down to 12V or so, but 9V is probably pushing your luck. The specifications for your instrument may well give a few more clues.

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Do you mean that you have 2 _ 7.2 volt "D - sized" batteries? The classic "D" battery is of a particular size, and it is 1.5 volts (nominal).

The capacity of the batteries you have are important, as is the rate at which they discharge or can discharge. Rechargeable alkaline 9 volt batteries have very little capacity, and depending on the technology, may or may not deliver current at the rate of your original batteries.

You may also want to make sure exsiting batteries are wired in series in air/ga instrument. (most the time they are, but it is possible they are in parrelle to deliver more current or to last longer.) might want to make sure first. If device has plug in jack too, device voltage requirement most likely stamped on it.

Also search internet, ebay etc. for replacement 7.2 volt batteries from 3rd party supplier.

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I found my batteries. 2x 7.2v ni-cad. My charger output is 17dcv. Could this be why my batteries cracked? Do i need another charger with output of 14.4dcv?

You need more than 14.4 volts to force current into your battery pack, and the charger should limit the current.

I have samplers that use 3.6v AA batteries, so I can sympathsize. A fully charged lead acid battery is 14.2v or so. The earlier comment about how your batteries are wired in is important. They could be 14.4v out or 7.2v. A 24v lead acid with a voltage/power (PVM) controller is worth looking into.

Hi Mr. Smyth,

It depends on the design of the equipment but generally no for the 9v battery the voltage will be too low. You can check with the manufacture to see the acceptable range. 2) 7.2v batteries is the best way to go. You can use batteries that add up to 14.4v but what you will find is that the discharge curves of the batteries will probably not be the same and you will not get optimum performance of the new batteries. The last thing to consider is the Amp Hour (AH) rating of the battery string; it need to be the same or higher than the original batteries or you will not get as long as a run time.

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What type of gas are you sensing? If the equipment is classified for use in hazardous areas, you need to follow the manufacturer's manual and cautions. Different batteries will have different characteristics such as surface temperatures, max short circuit current, etc which could pose an explosion hazard.

As a rule of thumb, follow manufacturer's requirements, and if you're going to replace anything, make sure it's critical parameters are not exceeded.