Fluke 731B & 750A batteries

The 731B uses ordinary sub-C Nicads. nothing special about them.. don't bother getting the higher capacity Nicads.. the internal charging circuit isn't designed for them.

I have a Fluke 740A transfer standard that I'd like to find a suitable replacement for the 1.65V mercury cell inside it. It's a very large cell... a bit larger than a D cell.

Hi Dave, Thanks for the response.

What is the voltage used for the 731B? How many cells.

I would have thought it would be sealed lead acid.

Thanks Gary K4FMX

Hi Gary, The 731B uses 12 nicad cells for a total of 14.4 volts. I have a 731B manual, but not willing to part with it, since I have a copy of the instrument to accompany it. Might be willing to make a copy of it for you...

Email me directly and we'll talk.

You can buy an original manual for the 731B at

I would think that either the silver oxide cell (about 1.45V if i remember correctly) or the lithium cell (most are 3.0V but Tadrian has higher voltage cells) would be useful as local standards.

Hi Dave,

I sent you an email a few days ago. Don't know if you got it. I sure would like to get a copy of the 731B manual from you.

The 750A reference divider I ended up installing some AAA battery holders in the battery compartment and using 10 AAA cells. Seems to work ok. The current looks to be less than a micro amp when not in use.

I also have a fluke 540B thermal transfer unit. It uses a large mercury cell like your 740. I need to find a manual for it and determine what kind of batteries I can use in it too. In addition to the mercury cell it also uses rechargeable batteries. None came with it so don't know what they are yet.

Thanks for your help Gary K4FMX

Hi Gary, Sorry for the delay.. was very busy over the weekend, just didn't have time to respond till now. I can't offer anything on the 750A reference divider, however, I do know that the 540B uses 2 bundles of 10 sub-C nicads for 12.25 volts each. It also uses a 1.35 volt mercury cell N53T for the reference, but I don't know where you can find a replacement for that one. Mine is still operable, so I'm not in a bind for that yet. But I know the day is coming... As to the manuals... I'll email you offline.