Question - we had a battery crack open on a recent trip to Africa. It's a Watson (B&H) replacement for a JVC BN-VF823 7.4v ,2250 mAh. The case opened easily and I clipped the connections off the battery(s) and disposed of the cells. The data board and case are in excellent condition.

If you have a 170, you know the battery life is much less than desired.

Can I add a DC plug connector and use this as my dummy battery to power the camcorder with a higher cap external battery that's 7.4v ?

The board inside has a "B-" , "B+" , and a "BC" connection.

I understand the +/- but what do I connect to the "BC" ?

Yes you can. I have the LS300 not sure if they are the same or not but just like you stated the + goes to + and the - goes to -. I do have a pin out but you may be able to tell by the battery board which is which.

We also have an LS300. Much better battery life there - they just use different batteries. Not sure why JVC used these tiny batteries on the 170.
I'm thinking the "BC" connection if for the battery charge indication on the camera. The original pack had 6 x 3.7v cells and the BC connection was to 3+ and 3- ends all connected together.

yes that is referred as connected in Parallel. Can you see where the negative pole and positive pole was connected on the battery? t=you may be able to follow the tracer to the corresponding pin of the battery.

Edit: Ok I see your first post with the pic. Can you open and remove the board? If so you can follow the tracers to the pins.

In another forum the guy said he couldn't get the camera to recognize the setup without leaving the board in the system - but I'll only have the two +/- wires coming in.

I use a 12v external 6 amp/hr rechargeable Li-ion battery plugged into the DC in jack. No viewfinder readout of any kind but it lasts for ages in tandem with the normal camera battery.

Thanks ! That's another good option.

Think I solved the issue. Got the +/- connected and still had no voltage on the contact side of the battery. After some tweaking with the multimeter , I realized the ground was the missing link on the camera side of the battery. A little solder and a custom formed section of a paper clip was just the ticket. Soldered from the ground contact to a "G" contact on the board. Perfect voltage on the output side. "BC" terminal not connected. Camera displayed remaining battery time just like with the factory battery.

Tested it this morning in HD to extend recording times. Got both cards filled - 328 minutes recorded - and the camera was still powered up and running some 6 hours later showing 0 battery.
I used a VariZoom battery plate for Sony L series batteries with DC tap output and a Watson 970 battery.

Elvis has left the building !