disclaimer: Notes and images are strictly as-is, without any warranty or suggestions. Li-On batteries do contain Lithium (sic!) which reacts strongly with water, may burn and is therefor potentially harmful to you or your equipment. It seems pretty much common view that Li-On batteries are only reliable when equipped with an electronic control circuit within the battery pack. This info is just provided because I'm a touch unhappy with the opaque and/or vague information on Panasonic/Lumix G1 3rd-party batteries.

story

The G1 had been bought in October 2009 with a Panasonic DMW-BLB13E, 1250mAh, 9.0Wh battery, which works fine in the Panasonic DE-A49 charger and camera (body firmware 1.2).
Additional, a DMW-BLB13E, 5500mAh 3rd party battery was purchased. It was accepted by the G1, but didn't seem to work in the charger (blinking lights forever, measured output voltage going low until battery pack disables output).
At that point the 3rd party battery became useless and thereby available for internal inspection. After charging the pack for about 9h with 50mA (well below the maximum '1C' charging rate, and with ca 500mAh well below nominal capacity), first directly at internal contacts, then via the external contacts, it reached 8.4V at the external terminals and 4.17V at both the two internal Li-On packs. Nominal cut-off voltage for Li-On, as found in Wikipedia, is 4.2V-per-cell (apparently depending on Li-On technology). The voltage output at the external terminals seems fairly stable without load (before this charging it fell off quickly). However, the G1 refused to accept the battery ("This battery can not be used"). After some time and after putting it on the charger again, the G1 does accept the 3rd party. WIHIH ?
Btw, the 8-SOIC chip on the two-sided PCB is unmarked, or had its mark removed. The underside seem to feature some more SOT-23 packages, which have not been checked. I guess the serial (clock + data ?, SPI ?) interface could be debugged, but nop, no plans to do this here.

questions

• why is a 3rd party battery labelled 5500mAh, with practical the same weight (original 60g, 3rd-party 65g) ? This claims 4x more energy-per-weight than the original. Either Panasonic's technology is not up-to-date, or the 5500mAh is fictitious .
• why wasn't the 3rd party battery charged by the Panasonic DE-A49 charger ?
• does the DE-A49 charger interface via serial protocoll to the battery ? Does it write data to it ? Does it check the battery id ?
• Apparently, and contrary to other statements found in the web, the G1 1.2 firmware does check on the serial data within the electronics. I'm inclined to assume that the direct charging of the Li-On may have damaged the battery serial interface, so the G1 may not get any data at all from it now. Whereas the 1.4 firmware, as told on the web, may be actually checking the resulting contents of the serial data. This serial protocol on the two inner terminals seems to be a very murky, security-by-obscurity thing of Panasonic.

conclusion

It may have technological advantages to built electronics into a battery pack. However, the whole 3rd party issue with Panasonic batteries would not be such a drag, and the obscure market for 3rd-party would diminish, if Panasonic sold batteries at a reasonable price. 70 Euros ( =100 US$ for our pan-Atlantic folks) seems a bit ludicrous for a single Li-On pack these days.

written 15th January 2010, text and images are under the GNU_Free_Documentation_License.
Should you have more facts available on the details of the serial handshake, I'd love an email to fmue[AT]pab-opto.de .