Thanks a lot for the detailed answer Glen. I have looked in more detail into my machine and its rear connectors. It's a 21MX (2112A), and it has two battery holders at the back. The old batteries even came with it (!). On this machine the battery connectors are just two pronged, + and -, so no thermistor connection apparently. At first glance I thought two other 9 pin connectors were similar to the ones you described and needed to be wired up with the thermistors. But they apparently are totally different things, labeled POWER CONT IN and POWER CONT OUT. After a bit of bitsaver hunting, I gather these are for power control interconnection with optional I/O racks extensions. So I think I am thermistor free. I just need to find new small 12V lead batteries that fit. They are an odd "construction brick" form factor, standard modern gel batteries are too tall. Marc ------------------------------ Glen Slick <glen.slick at gmail.com> said: Subject: Re: HP 2113e Battery resistor I have only looked at the "B" version of the power supply as that is what I have in my 2117F. (Now that I think of it I'm not sure what version of the power supply I have in my 2113B). The details for that are covered in the 5061-1356 section of the 92851-90001_Jun79_9.pdf manual referenced below starting on page 84 of the PDF. As described in section 3-9 on page 105 of the PDF the Power Fail Recovery System (PFRS) option consists of the Battery Charger Board (A3A3) and the Battery Backup Board (A3A4) which are mounted internally in the power supply, and the external mounted Battery/Status Assembly. If the PFRS option is not present the Jumper Board (A3A4) is installed internally in the power supply instead of the Battery Charger Board (A3A3) and the Battery Backup Board (A3A4). If you open up your system far enough to remove the lid on the power supply you can visually inspect the installed boards to determine whether or not the PFRS option is installed in the power supply. The battery pack over-temperature thermistor is integrated into the battery pack. It ends up being connected to the TEMP1 and TEMP2 signals shown on the Battery Charger Board (A3A3) schematic Sheet 6 on page 136 of the PDF. If the PFRS option is not installed the Battery Charger Board (A3A3) is not present and there is nothing that would connect to the battery pack thermistor so it is not necessary for the operation of the power supply. If the PFRS option is installed but the thermistor or resistor equivalent is not connected the CPU will power on but will not be functional. I think all of the front panel lights turn on and none of the switches have any effect. It's been a long time since I looked at that in detail to figure out what was going on. I think some of the voltages are at the correct level, but maybe the memory voltages are not, and some of the power supply status signals (PSU?, PON?) indicate the power supply is not ready and that holds the system in the inactive state. -Glen ------------------------------