Battery already crapping out, ideas?

[Castellen]

Rechargeable lithiums are a good idea, but unfortunately the charge requirements of these cells are not compatible with the Ni-Cad charging on the Amiga motherboard.

Take the Panasonic manganese-lithium cell ML2032 for example.  The application note specifically says not to use the float charging techniques used with Ni-Cad, i.e. a trickle charge resistor connected to +5V.  The reason is that the battery needs to be charged with a terminal voltage of 3.0 to 3.3V, if this voltage is exceeded, the battery will be damaged.

An obvious way around this is to put a 3.3V zener diode across the battery so that the charge voltage is limited to 3.3V.

For the ML2032, it's recommended charge current is 2-3mA.
In the A4000D for example, the battery charge current is limited by R179, 1.2k ohms.
So charge current would be ((5V-3.3V)/1200) = 1.3mA which is a bit on the low side.
So if you were to decrease R179 to 560 ohms, this would then give a charge current of ((5V-3.3V)/560) = 3mA.

The cell's capacity is 60mA from memory, so if it was completely flat, it would take (60mAh/3mA) = 20 hours approx to charge.

The minimum data retention voltage of the RP5C01 real time clock is 2.2V and backup current is 15µA.
The ML2032 reaches this terminal voltage when it's discharged to approx 50% of it's capacity, so this gives an affective capacity of (60mAh/2) = 30mAh.
At a discharge current of 15µA, the battery backup time for a fully charged battery is (30mAh/15µA) = 2000 hours (/24) = 83 days (/30) = 2.7 months.

i.e. To use the ML2032 rechargeable manganese-lithium in the A4000D:
1. Replace R179 with a 560 ohm resistor (or just solder another 1.2k ohm resistor across the existing one to give you 600 ohms).
2. Connect a 3.3V zener diode across the battery terminals, obviously the cathode connects to battery+ and anode to battery-.
3. Connect the ML2032 cell in place of the old Ni-Cad or Ni-MH battery.

I might write an application note on this one day, maybe make up a kit & instructions with all the parts needed.  There's probably a slightly better way to do it as well, as there are problems using zener diodes at really low currents.  Unfortunately that requires me to think, so will maybe research it properly some other time.

In the meantime, you may have already seen some other notes on Amiga batteries and other things I've written here.

[Castellen]

I generally replace RTC batteries with the original Varta 3/V80H as well, but it's a fact they only have a service life of around 6 years max.  After that, they can start leaking at any time.  So as long as you replace the battery every 6 years, it's good enough.

When I'm doing battery replacements in customer's machines, I have a pre-printed label to stick on the back showing the battery replacement date and the replace by date.

@Amiduffer
I might look at setting up a "do-it-yourself kit" of some sort then over the next few weeks/months as well as writing an application note/tech article for my webserver.
It's nearly summer here in NZ which means the end of yet another snowboarding season :-(  On the plus side, I can actually get some work done now, so will see if I can fit it in with my other summer projects.

Send me an email so I have your contact details.  I can probably do something cheap as a product trial in exchange for some feedback email, etc.