Modding a 900MHz Panasonic phone

[Pete R]

It's time for a new battery in our 900MHz Panasonic TC1741,
and we'd like to switch from the stock 3 x 600mAh NiCad
batteries to something with more capacity, maybe 3 x 1000mAh
or 3 x 1200mAh.

The handset has a battery indicator, and we'd like to know if this
indicator works by simply keeping track of how long the phone
has been used since the last recharge, or if it actually measures
battery strength. If it's a dumb indicator then it will start beeping
for a recharge well before the new, higher capacity batteries are
discharged.

We emailed Panasonic tech support and their answer was, "We
don't know". Has anyone tried this with one of their 900MHz
phones?

Thanks.

 

[Ken Weitzel]

It's time for a new battery in our 900MHz Panasonic TC1741,
and we'd like to switch from the stock 3 x 600mAh NiCad
batteries to something with more capacity, maybe 3 x 1000mAh
or 3 x 1200mAh.

The handset has a battery indicator, and we'd like to know if this
indicator works by simply keeping track of how long the phone
has been used since the last recharge, or if it actually measures
battery strength. If it's a dumb indicator then it will start beeping
for a recharge well before the new, higher capacity batteries are
discharged.

We emailed Panasonic tech support and their answer was, "We
don't know". Has anyone tried this with one of their 900MHz
phones?

Thanks.

Hi Pete...

I don't "know" either; but I'm willing to bet you a
zillion bucks against a stale donut that it's just
monitoring voltage.

(I like the chocolate covered ones

Take care.

Ken

 

[Pete R]

Hi Pete...

I don't "know" either; but I'm willing to bet you a
zillion bucks against a stale donut that it's just
monitoring voltage.

(I like the chocolate covered ones

Take care.

Thanks Ken. So if that's the case, the higher capacity batteries
won't cause the phone to beep for a recharge prematurely?

 

[jakdedert]

It's time for a new battery in our 900MHz Panasonic TC1741,
and we'd like to switch from the stock 3 x 600mAh NiCad
batteries to something with more capacity, maybe 3 x 1000mAh
or 3 x 1200mAh.

The handset has a battery indicator, and we'd like to know if this
indicator works by simply keeping track of how long the phone
has been used since the last recharge, or if it actually measures
battery strength. If it's a dumb indicator then it will start beeping
for a recharge well before the new, higher capacity batteries are
discharged.

We emailed Panasonic tech support and their answer was, "We
don't know". Has anyone tried this with one of their 900MHz
phones?

Thanks.

If you have a variable DC supply (or make one from a battery and a pot)
you can monitor the phones indicator activity vs. voltage.

BTW, anybody know how those battery meters work? IMO, they could hardly
show actual % of charge based on voltage, given the normal discharge
curve of nicad and nimh batteries. OTOH, I've noticed that once the
battery meter starts to show any decrease, it's time to recharge. Once
the voltage starts to go down at all, it's nearly exhausted.

jak

 

[Franc Zabkar]

It's time for a new battery in our 900MHz Panasonic TC1741,
and we'd like to switch from the stock 3 x 600mAh NiCad
batteries to something with more capacity, maybe 3 x 1000mAh
or 3 x 1200mAh.

The handset has a battery indicator, and we'd like to know if this
indicator works by simply keeping track of how long the phone
has been used since the last recharge, or if it actually measures
battery strength. If it's a dumb indicator then it will start beeping
for a recharge well before the new, higher capacity batteries are
discharged.

We emailed Panasonic tech support and their answer was, "We
don't know". Has anyone tried this with one of their 900MHz
phones?

Thanks.

I have an old KX-T4027AL-W/AUS cordless Panasonic phone whose original
KX-A36A (3.6V ~400mAh) pack has been replaced with a much larger pack.
This particular model detects the battery voltage which means that the
talk and standby times are dependent on the mAh rating. The only
downside is that I can't get the battery cover back on, so I've had to
retain the pack with double-sided tape.


- Franc Zabkar

 

[none]

I have an old KX-T4027AL-W/AUS cordless Panasonic phone whose original
KX-A36A (3.6V ~400mAh) pack has been replaced with a much larger pack.
This particular model detects the battery voltage which means that the
talk and standby times are dependent on the mAh rating. The only
downside is that I can't get the battery cover back on, so I've had to
retain the pack with double-sided tape.


- Franc Zabkar

Have you considered switching to nickel metal hydride?
I've replaced most all of the rechargable modules in my cordless
phones with them and they've given much longer run times and seem to
charge just fine with the stands charging circuits.(Also replaced the
nicads in a pair of wireless headphones with nimh and am getting
nearly double play time as compaird to the old nicads.)
The cordless phones I have are Unidens, GE, Sony, Toshiba and
Panasonics.(got 'em in just about every room of the house.)
Correct about the battery indicator function, reads power levels and
starts beeping when current levels drop too low.
If you can't find the particular module for your phone in nimh you can
always match battery size and number with other mod#'s of modules and
simply switch the leads/connector off your old battery. a simple
solder job.

 

[Pete R]

Have you considered switching to nickel metal hydride?
I've replaced most all of the rechargable modules in my cordless
phones with them and they've given much longer run times and seem to
charge just fine with the stands charging circuits.(Also replaced the
nicads in a pair of wireless headphones with nimh and am getting
nearly double play time as compaird to the old nicads.)
The cordless phones I have are Unidens, GE, Sony, Toshiba and
Panasonics.(got 'em in just about every room of the house.)
Correct about the battery indicator function, reads power levels and
starts beeping when current levels drop too low.
If you can't find the particular module for your phone in nimh you can
always match battery size and number with other mod#'s of modules and
simply switch the leads/connector off your old battery. a simple
solder job.

Thanks, that's what I was hoping to hear. Sounds like I won't
have to settle for 1000 or 1200mAh batteries -- I could get 3
2500mAh NiMH's with solder tabs? That would be way cool.
Recharge once a month instead of every week!

 

[Ken Weitzel]

Thanks, that's what I was hoping to hear. Sounds like I won't
have to settle for 1000 or 1200mAh batteries -- I could get 3
2500mAh NiMH's with solder tabs? That would be way cool.
Recharge once a month instead of every week!

Hi...

If you do decide to go that route, keep in mind that
there's an enormous difference in the self discharge rate
between nicads and nimh's.

Perhaps if you have one of those teenagers that talks on
the phone 16 out of every 24 hours it would be to your
advantage, but otherwise not so sure...

And - if you do use nimh's, make sure that you do *good*
quality work. The internal impedance is so low that
they're quite a fire/burn hazard. I still have a scar
on my leg from stupidly putting a couple of 1400 ma aa's
in my pant pocket. (I use 'em in digital cameras)

Finally, remember the charge times. If it takes you overnight
to re-charge your 600's; it will take you 4x's as long to
charge up 2500's.

I suggest considering that though nicad's and nimh's are
virtually the same price now - no manufacturer to the
best of my knowledge has built them into any.

Just my 2 cents worth.

Take care.

Ken

 

[Lee]

I suggest considering that though nicad's and nimh's are
virtually the same price now - no manufacturer to the
best of my knowledge has built them into any.

My Samsung Dect phone came with an NiMh pack.

Lee

 

[Doug McLaren]

| If you do decide to go that route, keep in mind that
| there's an enormous difference in the self discharge rate
| between nicads and nimh's.

By enormous he means about 3x. NiMH cells seem to self-discharge at
about 3x the rate of NiCd cells. Of course it'll depend on the cells
themselves.

| Perhaps if you have one of those teenagers that talks on
| the phone 16 out of every 24 hours it would be to your
| advantage, but otherwise not so sure...

I'm guessing it would be. These phones tend to die in a week or so
without charging with the stock batteries.

| And - if you do use nimh's, make sure that you do *good*
| quality work. The internal impedance is so low that
| they're quite a fire/burn hazard.

NiCd cells have even lower internal resistances.

| I still have a scar on my leg from stupidly putting a couple of 1400
| ma aa's in my pant pocket. (I use 'em in digital cameras)

Really? I've put lots of AA NiCd and NiMH cells in my pocket loose
and while I should know better, I still do it from time to time. I've
occasionally had them short out against my keys or something similar,
but in every case I just noticed that my pocket was getting hot.
Sometimes very hot, but never anywhere near hot enough to burn me.
Maybe my keys just didn't make a good enough connection.

Now, if you were to bang the cell hard enough to short internally,
then you've got a hot steamer going on.

| Finally, remember the charge times. If it takes you overnight
| to re-charge your 600's; it will take you 4x's as long to
| charge up 2500's.

Longer, actually -- don't forget about the self discharge rate.

| I suggest considering that though nicad's and nimh's are virtually
| the same price now - no manufacturer to the best of my knowledge has
| built them into any.

Huh? I'm not sure I understand what you're saying here.

Lots of devices have NiCd cells, and lots have NiMH cells. Including
cordless phones.

Personally, since NiMH and NiCd cells have very similar charge and
discharge curves, I suspect that simply replacing the 600 mAh NiCd
pack with a 2500 mAh NiMH pack in a cordless phone will work perfectly
95% of the time. Yes, charges will take much longer (if starting from
a dead battery) and the self discharge rate will be higher (but I
suspect that the added capacity will more than make up for that
assuming that the phone is actually on when not in the charger.) I
suspect that even the battery charge indicator will still work, though
it might become somewhat inaccurate (i.e. it may not be as linear as
it was before, if it was ever linear (it's difficult (at best) to
accurately determine the state of charge of a NiMH/NiCd cell based
only on the voltage now. You can make a guess, and you can tell that
the battery is almost dead, but before that, it's pretty much a
crapshoot, especially if the battery was not fully charged before.)

The only complications I see are if the phone quick charges -- if it
claims to be able to fully charge the battery in a few hours, then
there's a good chance that either 1) it won't fully charge the
battery, or 2) won't detect when it's full, and will keep charging.
But in my experience, most cordless phones are slow charged, which
will be OK.

 

[Pete R]

| If you do decide to go that route, keep in mind that
| there's an enormous difference in the self discharge rate
| between nicads and nimh's.

By enormous he means about 3x. NiMH cells seem to self-discharge at
about 3x the rate of NiCd cells. Of course it'll depend on the cells
themselves.

We've noticed enormous differences between cell brands, and
even between capacities within the same brand. E.g. our
PowerEx 1800's self-discharge very quickly (full to almost
dead within 30 days), while our Panasonic 2100's can go
almost two months and still have enough of a charge to be
usable.

The other problem we've had with PowerEx's is consistency.
In a given set of four -- all with the same rating -- we've seen
very wide variances in both capacity and self-discharge rate.
The Panasonics are far more predictable and consistent.

| Perhaps if you have one of those teenagers that talks on
| the phone 16 out of every 24 hours it would be to your
| advantage, but otherwise not so sure...

I'm guessing it would be. These phones tend to die in a week or so
without charging with the stock batteries.

Exactly right. We have to recharge every week, pretty much
regardless of how much usage we put on the phone.

| And - if you do use nimh's, make sure that you do *good*
| quality work. The internal impedance is so low that
| they're quite a fire/burn hazard.

NiCd cells have even lower internal resistances.

By "work" are you referring to the quality of the solder joints?

| Finally, remember the charge times. If it takes you overnight
| to re-charge your 600's; it will take you 4x's as long to
| charge up 2500's.

Longer, actually -- don't forget about the self discharge rate.

The phone fully recharges its stock 600mAh batteries in 6 hours,
so we're assuming a 100mA voltage (Panasonic said they "don't
have this info"). 2500mAh's would take roughly 25 hours to
recharge, but since NiMH's don't have memory problems we
could use the phone and just put it back on the base to continue
recharging when we're done.

The only complications I see are if the phone quick charges -- if it
claims to be able to fully charge the battery in a few hours, then
there's a good chance that either 1) it won't fully charge the
battery, or 2) won't detect when it's full, and will keep charging.
But in my experience, most cordless phones are slow charged, which
will be OK.

The TC1741 doesn't have a quick charge option, and we're
pretty sure it doesn't detect when cells are fully recharged.
If anyone knows for sure we'd love to know.

Thanks for the responses, guys. Very helpful.

 

[Franc Zabkar]

Have you considered switching to nickel metal hydride?

I will in future. I used NiCads because I already had them.


- Franc Zabkar