It amazes me again and again what people do.
Putting LiIon packs in place of NiMH is just haphazard, might result in a blaze.

Search on good electronics distributors' websites (RS, Farnell, Mouser, Reichelt, Conrad, just to name a few) and search for NiMH cells with solderable fins. Then build your pack. Don't worry about the smaller size of modern batteries, instead be happy you got room for wiring etc.

IF you use Lithium cells with integrated charge circuit and overcharge and discharge protection then this might be possible. But as retardware said: You need to be sure of what you're doing or you can cause a fire that harms you or others. Generally this is a bad idea and I would also stick with NiMh batteries.

retardware wrote:

It amazes me again and again what people do.
Putting LiIon packs in place of NiMH is just haphazard, might result in a blaze.

Search on good electronics distributors' websites (RS, Farnell, Mouser, Reichelt, Conrad, just to name a few) and search for NiMH cells with solderable fins. Then build your pack. Don't worry about the smaller size of modern batteries, instead be happy you got room for wiring etc.

Thanks for both answers, of course I was thinking the same thing when I saw that guide for restoring the battery, that's why I asked if any safe solution would exists for this very old phone that would be nice to collect.
I found that looking more there're seller having Ni-Mh 500mah cells batteries I was looking for, they call it "prismatic batteries" and similar size even if they are quite expensive.
Having some old still perfect phones li-on 3,7v batteries it'd sounds like a good idea to use lighter, more available and with more capacity li-on batteries but I imagined it wouldn't be possible.😀

My Nokia 9110's batteries are almost dead too. Maximum 15 minutes capacity left.

I looked into a battery pack (a "compatible" one):

As you see, there is charging circuit inside, and the battery has no label.
Will open an original Nokia battery pack soon, too.
Maybe there is some hint on the battery that makes easier to look for an exactly compatible replacement.

retardware wrote:

My Nokia 9110's batteries are almost dead too. Maximum 15 minutes capacity left. […]
Show full quote

My Nokia 9110's batteries are almost dead too. Maximum 15 minutes capacity left.

I looked into a battery pack (a "compatible" one):

As you see, there is charging circuit inside, and the battery has no label.
Will open an original Nokia battery pack soon, too.
Maybe there is some hint on the battery that makes easier to look for an exactly compatible replacement.

On the compatible 1610 battery there were good high quality brand japanese ni-mh not-working cells and just the wires where at the end there's the protection resistor for the temperature (I think).
The ni-mh batteries I want to buy for the replacement are generic brand only problem it looks there's only the metal pin at each side so maybe difficult soldering but still the best and easier solution for collecting this great phone.

I was thinking to try these Ni-Mh batteries on rsonline seller:

buying the model with already packed four ni-mh botton battery (4,8v 510mah) and adding a single one botton battery (1,2v 510mah) to get the end 6V battery beside its price, still a bit high that I thought.
Do you think that the current/capacity difference would be a problem? And what about the chargin voltage considering the 10v of the original charger?

Thank

The Germany-made battery pictured is of very high quality, and this has its price.
The capacity difference does not matter, as the charging process is voltage-based.

RS is not cheap. You can look around for reputable distributors in your local area, too.

You were talking about a 10V 750mA wall wart as cellphone psu? Usually the cellphones have charging electronics.
Or are you really talking about a dedicated battery charger? Doesn't it have charging electronics that feeds appropriate voltages to the battery?

retardware wrote:

The Germany-made battery pictured is of very high quality, and this has its price. The capacity difference does not matter, as t […]
Show full quote

The Germany-made battery pictured is of very high quality, and this has its price.
The capacity difference does not matter, as the charging process is voltage-based.

RS is not cheap. You can look around for reputable distributors in your local area, too.

You were talking about a 10V 750mA wall wart as cellphone psu? Usually the cellphones have charging electronics.
Or are you really talking about a dedicated battery charger? Doesn't it have charging electronics that feeds appropriate voltages to the battery?

Yes the price of those batteries are quite high to get 6 volts pack. But also the identical original ni-mh batteries are equally expensive but probably chinese made.
The 10 volt charger is the original wall charger by Nokia having a strange size connector compared to the bigger one of the old Symbian S60 v1 phones and the very thin connector of the later S60 3rd phones.750mah looks like a fast charger.

What confuses me much is when people mix mAh and mA.
The first one is battery capacity (milliamperes/hour, 1000mAh indicates it can deliver 50mA over 20 hours).
The second one is just how much current a power supply can deliver.

Without having seen the phone and the power supplies/chargers, I still have the feeling that there is internal charging circuitry to adequately charge the battery pack. The time when batteries were charged by just connecting to a fixed-voltage DC supply were looong gone already in the 1990s.

I lost the charger to my 1610 so I soldered on a 9V battery compartment with a battery that has a microUSB port on it for charging. It's not the best but it works. Might redo it a bit more neatly in future. A normal Duracel 9V battery will also work, but only for standby. Soon as you make a call it drops, I suspect it does not have enough amps to pull the phone, whereas the rechargeable does.

At the end the 1610 phone I have ended up not finding a solution cause I rebuilt a battery buying the single Ni-Mh cells but unfortunately one of the module is not working or charging but now to replace that single cell I've to cut the plastic I already fixed and I suppose risking to break it. Anyway it does work in standby but the charging can't charge all the cells and after hours it still gives the low battery signal but at least it can stay in standby working without the charger, I suppose at a lower -1.2v voltage. Anyway one day I'll try again, I shoud also change the ear speaker cause the voice quality became very bad. I don't think it was great in its time but not that bad.