TM742A battery replaced – finally

By way of a short history lesson, 16 years ago my employer decided I was surplus to their requirements and gave me extra money to finish up. I took some of that money and invested it in a new Kenwood TM742A 6m, 2m & 70cm mobile rig. Since then I have used this rig a lot, and when I was doing field work it was in the car and in use every day. It has been to every SRESU activity I have done since 1996 and has never let me down.

Inside these rigs, like so many rigs of that era, is a small 3.0 Volt lithium battery that backs up the microprocessor, channel memories and such.

Lithium batteries are generally regarded as being good for about 7 to 10 years. After that time they have discharged too much and the memories start to become corrupt. I have even read of these batteries leaking and damaging the circuit board they are on beyond repair.

In July 2006 I decided that 10 years was a good length of time for the battery in my TM742A so I bought a new battery from Jaycar and resolved to replace it. The radio had been working fine with only an occasional hiccup but it was something that needed to be done.

2006 came and went; battery not fitted. 2007 and 2008 came and went; no battery fitted, 2009 and 2010 came and went; battery still not fitted.

Today I had planned to get on the roof and look at my dipole antenna but it was raining. So I decided to have a go at fitting the ‘new’ battery into my TM742. The TM742 group is a great source of information and I had downloaded instructions on how to replace the battery so I was fairly confident.

The task flowed well, as described in the instructions and, apart from my battery being slightly different from the existing battery, went without a problem. I even added a piece of paper with the date on it so I remember when it was done when next I have to change it.

Hopefully I will get 5 or more years out of this battery. Although to be fair it has already sat on the shelf for 5 years and if it has only a 7 year life then it won’t be long before I am doing it again.

Old battery in situ on left side of chassis

Board with new battery – note the added black wire (on the negative side of the battery)


Solder points for battery
Solder points for battery

New battery on left side of chassis


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9 Responses to TM742A battery replaced – finally

  1. Andrew Squires says:

    Peter do you have detailed instructions on changing the battery ? You give a link to Yahoo but it must have expired ?
    Thanks Andy VK3AS

  2. Marvin Storey says:

    Thank you for the excellent information on Replacing the TM742A lithium battery. I too have the 6m, 2m, and 70cm model that I purchased over 10 years ago. The battery just died. I have held off for two weeks after taking the radio partially apart but didn’t want to go any further in the wrong direction. Now as soon as the replacement battery that I have ordered arrives, I will dive into it. Will also check into the TM742 Yahoo group that I didn’t know about.

  3. Phil says:

    I know this question is late but I am now just trying to replace the battery in my 742. I also cannot get the instructions from the blog. Would it be too much trouble to forward the battery replacement instructions you got to me?
    Thanks for your help

  4. Scott McCreight says:

    I also have a Kenwood TM-741A that has been dormant for 12 or so years. Will not hold memory now so I am thinking that the 3.0V Cell in main unit is dead. I am in need of how to take a part the board that houses the Lith 3.0V cell. Also hear that there is another battery? Where and what for? I am looking forward to getting it back n the air soon. Thanks Scott de N5ZL

  5. Paul says:

    I was interested in reading this blog article as I have a (similar but older) TM-741A that requires battery replacement. I am unable to get the disassembly instructions from the Yahoo TM-742 group as, frankly, to join Yahoo is asking for more information than they actually require (data mining?). Do you know of anywhere else this information is available? Any info would be much appreciated.

    By the way, I am retired now but one of my last projects was involvement submitting the winning bid to replace the Air Traffic Control systems in the Australian Control Towers. :)


  6. Daniel says:

    Thank you for the info. I also have one that has 144, 220, and 1200 mhz modules. Great radio.

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