Any expert on NEC Mobilepro batteries?

[theancientone]

I took apart my battery pack on my 900, as I noticed that after few years in storage, even after fully charged, it would last for less than an hour (I think these new were like 8h?)
Now the interesting thing is that I opened the pack and the voltage is 7.4V as the device is telling me that there is 0% power left... This is wrong, as the battery is working just fine, but I keep getting the low battery messages and the battery capacity goes between 10% and 0%

Is this normal with these batteries? They are simple 18650 so I am planning to swap the cells at this point, but what is concerning me is how do I reset the battery chip ? The board in the battery pack seems to be a smart one, and not just a plain charging circuit, so I assume there is a way to reset it so it will read more accurately the battery capacity? I am concerned I go all the way to rebuild the battery and then it will still behave the same as with the old batteries

 

[theancientone]

So I replaced the cells; put everything together and the voltage at the pins of the battery is right... But the 900C now seems to not see the battery at all. I see the orange light as if it is charging, but it stay at 0% when I look at the battery capacity. Is there somehting that has to be done to reset the battery chip? Some batteries need to short the battery management pin to reset, not sure if this is the case with this battery too?

Is there anyone here that have the 900 and did a cell swap? Curious to know if it just worked for you or not.

 

[GiGaBiTe]

You'll have to research your battery controller IC and see if there's any publicly available information on it. Many smart batteries have programming that counts the charge cycles and also detects any faults or tampering with the battery pack. I've seen more than a few with kill switches that will put the pack into a permanently failed state if it detects any tampering with the circuit.

All of this information is generally stored in some EEPROM somewhere on the pack board. If you're unlucky, it can be inside the battery charge chip itself.

 

[theancientone]

Thanks; I thought others would know already as these handheld were quite common. After keeping the device off for a while, it still show no battery but now it show 20% left in the battery... I am not sure that the chip is locking itself with a kill switch otherwise it would not show 0% and now 20%. tried to short the various pins to see if it has a reset pin like with some Dell batteries, but nothing happened. It really sucks that we can't build our own battery packs to be honest

 

[GiGaBiTe]

Companies that sell the devices don't want the liability. They already have problems with their own battery pack designs going on fire and losing millions/billions of dollars from lawsuits over them. They also have to deal with substandard and/or counterfeit battery packs that get attributed back to them and also lose tons of money from lawsuits. Governments also breathe down their necks to get it right the first time because planes have crashed due to lithium battery fires.

I used to know a middle manager that worked at Dell. They had (and probably still have) teams that investigate aftermarket batteries for potential litigation to stop the more dangerous ones from being distributed. But it's like playing whack-a-mole, you get rid of one for three more to come up.

I'm sure there are technically minded people in those companies that want to allow users to make their own battery packs, or repair existing ones, but it's just too much liability.

As for building your own pack, you can, you just have to reverse engineer the charge controller and figure out how it works. I've reverse engineered a few battery packs for devices that no longer had replacements available. Unfortunately, unless someone has done it for your specific device, you have to start from scratch.

 

[theancientone]

I hear you, and in the end batteries blow up more easily than anything else. Although if you consider the "right to repair" in the mix, and put a disclaimer that modifying the battery means risks and you take those, then it should work it out After all if you use a non-standard AC adapter you risk to damage the device too, , but most devices use the same plug and for most part the same specs. I saw people blowing up their devices because they got wrong AC adapters, although nobody really ended up with a lawsuit. I still have to fight the urge to make fun of people writing on plastic bags "do not wear on your head, you may suffucate".

I think I found a close-enough technical document about the chip I see on the battery; so at this point it is just a matter to find a hook to get on that board and start to poke around the rom, to see what is going on. I found a device online that can rewrite chips from batteries, but it cost like 500 dollars, and that is a bit hard to justify for just one or two battery packs :D