The 3rd edition service manual shows BT601 on the schematic as 3 Volts, however the parts lists in that manual shows it as originally being a 2.9V battery with the list of parts changes indicating that it was later changed to 3.4V, and that the new battery is not compatible with the original resistor network. Just to confuse, an earlier manual shows that same battery in the parts list as 3V, and just to confuse further both parts list refer to the battery as BT501 instead of BT601. These batteries are described in the parts list as Lithium Sulfur Dioxide. There's a bit more information here..... http://www.eevblog.com/forum/blog/eevblog-426-hp-3457a-multimeter-teardown/ The text only version on archive.org of an old SAFT catalog shows this for the LX-1634.... LX1634, 2 /3A, 3.0, 0.85, 0.660, 16.8, 1.380, 35.1, 0.49, 14.0, S.GTM.FU. Sort of bring your own units but it does look like 3 V. Further searches on LX-1634 might prove beneficial. Regards Nigel GM8PZR In a message dated 24/01/2016 20:17:54 GMT Standard Time, drkirkby@kirkbymicrowave.co.uk writes: I've got a HP 3457A 6.5 digit multimeter - S/N 2703A04579. It's working fine, but I'm aware the battery must be at least 11 years old, as I first bought the meter 11 years ago. I suspect its due for a change. I'm trying to find a *reputable* source for a replacement. I want to avoid eBay, due to the number of fakes on there. Opening the meter up, I see the PCB shows "BT 601". There's no name on the battery I can see, but the type number of LX 1634. The voltage measured on my 4.5 digit handheld DVM is 3.03 V. Googling around https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/topic s/48964 would suggest the battery was made by Saft and is a Lithium-manganese dioxide (Li-MnO2). The size appears to be known as 2/3A. One source suggests a replacment is the Panasonic BR-2/3AE2SP Mouser's uk site http://www.mouser.co.uk/ says shipping is restricted, so only available in the USA. The nearest I've found to anything remotely suitable is actually a 3.6 V battery "CROMPTON ETERNACELL T32/8AA8F Battery, Single Cell, Lithium Thionyl Chloride, 2100 mAh, 3.6 V, 2/3A, Axial Leaded, 16.3 mm" http://uk.farnell.com/crompton-eternacell/t32-8aa8f/battery-lithium-2-3aa-ax ial-lead/dp/774017 I'd rather not fit a higher voltage battery, although given it provides power to some 5 V static RAM, I would not expect it to be a problem. That said, I believe when on mains power this battery is not needed, so there may be some circuitry that would not like a 3.7 V battery. When power is on the unit, there is 4.88 V across the static RAM. As mains is reduced, so the voltage drops to about 2.8 V. I think there must be a Schottky diode that stops the battery being drained when the mains power is on. The battery needs to have either very thin pins or wire-ended. Some I have seen have tags a 2~3 mm wide, which will not fit in the PCB. Others have 3 terminals, which stops you putting it in the wrong way around, but they will not fit properly on the PCB. In applications like the 3457A, when the SRAM needs to be kept alive when power is off, I wish HP would have put two batteries in holders and diode -OR'ed them. If they had done that, one could just pull out a battery from holder A, and put a new one in B. Then when B gets old, put one in A. My first problem though is finding a suitable battery. Next problem is changing it without losing the RAM contents, but I don't think that's a big deal. The 3.6 V Lithium Thionyl Chloride is very tempting, as it has a higher capacity than the Lithium-manganese dioxide and they have a very low self-discharge (1%/year). I'm just not overly happy about fitting a higher voltage battery than it is supposed to have, but phyysically it fits, and I can get one easy enough from Farnell in the UK. Dr. David Kirkby Ph.D CEng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK. Registered in England and Wales, company number 08914892. http://www.kirkbymicrowave.co.uk/ Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please) _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.