Motorola microtac battery

[Land Rover Fan]

The only reason I put them in removable holders is so I can charge the batteries outside the case.

[Mark1960]

Originally Posted by Land Rover Fan

Could removing the antenna help?

Also I need to have it working quite soon.

Probably best to reduce any series resistance from the batteries first.

Removing the antenna is not likely to be any better unless its a short circuit.

You could try an external power supply, with 1,000uf cap close to the battery contacts. Maybe try the capacitor with the batteries.

[Land Rover Fan]

Ok, one issue, I don’t have a external power supply .

[Land Rover Fan]

And how do you reduce battery resistance?
By the way I have another original NiCad battery which holds about 5 mins of charge, and I don’t get any issues with that.

[Mark1960]

Resistance external to the cells might be improved by using thicker wires and better connections to the cells. Internal battery resistance would need to change to better cells.

A large capacitor close to the battery contacts of the phone would reduce the effective resistance.

With the working battery connected, can you measure the voltage at the contacts with a scope? This should show the voltage drop during tx burst, 1 in 8 mark space ratio at about 217 hertz in a call, probably only for a short time during initial connection to the base station. Then see how this compares to your rebuilt battery.

[Mark1960]

Factory used HP battery emulator power supplies, with voltage sense at the battery contacts. This would have been around 1995 for the 7500 so memory is a bit unreliable.

[Land Rover Fan]

Hmm, I don’t have a scope unfortunately but I might try the capacitor…

[Land Rover Fan]

On the multi meter, it shows that the new battery voltage drops from 6.65v to 6.45v
On the original battery the voltage is 6.27v and doesn’t drop at all. The phone only powers off when it gets reception.

[Land Rover Fan]

Also, when it scans for signal the voltage drops to 5.95v and 5.80 when it boot loops.

[Land Rover Fan]

What do you think I should do? Different cells?

I would like to get this phone working as soon as possible.

[Techman]

It sounds like there's too much source impedance in the supply. Either the cells aren't up to the job (were they 'all' brand new? it only takes one bad one to muck things up) or there's resistance in the contacts of the holder/s.

[Land Rover Fan]

Yes all the cells are new aaa battery’s.

[Techman]

Originally Posted by Land Rover Fan

The only reason I put them in removable holders is so I can charge the batteries outside the case.

I think you've got your answer. It's either that the cells, even though new, are not up to the job, or it's resistance in the holders or the wiring to them, which is more likely. You need to have them hard fixed/wired, ie, soldered together in a thing like that and arrange for them to be charged as one complete battery.