Motorola microtac battery

[Land Rover Fan]

Hello,
I have recently acquired a Motorola microtac 7500 and i would like to know what is the best way to put new cells in the battery? I would like to do this with not destroying the battery case, also I would like to use the original charger without modifying it.

Any help much appreciated.

[Land Rover Fan]

Also the antenna is broken.

[Cobaltblue]

Did you see this :

https://www.youtube.com/watch?v=OWEHOeQghU8

Butchers it a bit but I an sure you can achieve the same result without so much butchering.

Cheers

Mike T

[Land Rover Fan]

Very interesting (and destructive!) the only thing is he modified the charger to get the right voltage for his Nokia batteries.

[agardiner]

I believe you can carefully open the battery pack and replace the cells? Photo attached of the internals of the pack; uses standard AAA rechargeable.

Note - I haven't tried myself.

[Pamphonica]

There seems to be a lot of information about rebuilding these batteries.
Like this: https://www.mobilecollectors.net/forum/viewtopic.php?f=4&t=111
If you need rechargeable batteries welded together to form a pack for you to put into your casing, I have a chinese battery welder that does an excellent job. PM me if interested, and you can supply the batteries!
-Jeremy

[Jon_G4MDC]

I did this once for a Motorola GP300. It worked but the case was never right afterwards.

I found a replacement amongst this lot and I am very pleased with it. The price was not much more than the cells would have cost and it came with a new pocket clip to boot.

Maybe you can find one suitable. There are an awful lot to sift through. Separate section for mobile phone batteries but they seem geared more to modern smartphones.

https://www.fusionbattery.co.uk/collections/two-way-radio-battery?page=57&sort_by=title-ascending

[Land Rover Fan]

Ok I have cut off the back of the battery and removed the old cells. I have ordered a 4 and a 1 aaa battery holder to go in the old cells place.

[Land Rover Fan]

Another thing what does the little switch do on the back of the battery?
On another battery I have which still has the original cells , it doesn’t seem to make a difference when you power up the phone?

[arjoll]

My first two cellphones were MicroTACs - a 1950 then an Ultra Lite, both on the Telecom NZ 025 analogue AMPS 800 network. Replaced with a Nokia 5120 around 1998 but I kept the Ultra Lite in a car kit until CDMA coverage overtook AMPS.

From memory that "switch" was just so you could keep track of which battery was charged when you had multiple batteries. Everyone at work who was issued a phone also had a dual charger and extra high capacity battery as part of the standard E&Y package from Telecom.

[Land Rover Fan]

Oh thank you very much, it’s interesting to hear someone who had one back in the day!

[arjoll]

I found some random bits of the car kit when I did some tidying in the workshop a few years ago - I'm pretty sure I threw them away but there's always the risk my hoarding instincts got the better of me!

[Land Rover Fan]

Hello all, I have repacked the battery! In the original cells place I have put 5 aaa 1.2 volt rechargeables. Unfortunately the phone ether boot-loops or switches off after a few seconds.
The multimeter shows 6.58 volts. Is this too much?

[Land Rover Fan]

Ok just checked the individual battery voltage, don’t you all think that 1.33 volts is a bit high for a 1.2 volt rated?

Also I have put 3 of them in a torch to try and discharge them.

[wave solder]

I.33v does not seem high at all. Batteries often have a higher terminal voltage than their marked nominal value, for example a 12v car battery is normally 12.6V

[Land Rover Fan]

Oh I have discharged the battery’s a bit down to 1.21 volts each and now the phone says “low battery” (sigh) so I wonder why it was switching off before? I will include a photo.

[Mark1960]

The GSM microtacs monitor the battery supply voltage during transmit bursts and record low battery or switch off if this is too low. The replacement cells may have too high an internal resistance compared to the expected battery performance. This could also be caused by the damaged antenna as this might cause the PA to draw higher current during transmit bursts.

[Land Rover Fan]

Oh ok, I have noticed it switches off as soon as it finds signal. What do you think I could do?

[Land Rover Fan]

Could removing the antenna help?

Also I need to have it working quite soon.

[Graham G3ZVT]

I noticed you said you were using battery holders with their inevitable series resistance.
I would have soldered the cells together with short wire links. Ideally metal spot-welded metal strips should be used, but solder has always worked for me if done quickly.