Before I switch over to a Bluetooth Low Energy solution I was ordering a new PCB (v1.3 see on github) with some added features:

• main power switch to fully disconnect the battery
• 250 mA fuse to make sure the anklet can’t be aflame
• a small push button to start calibration process and future use
• new “battery connector”/pin headers in position with Nokia 2600 battery terminals
• micro match connector to disconnect the motors if needed

I hope I will get the order from oshpark.com in three weeks (shipping time to europe). I will use my old stencil to get only the LSM303D on the board the other components could be easily added by soldering iron.

It’s interesting if the battery directly under the magnetometer IC is a problem. It should depend on the potential reservoir of ferromagnetic materials in the lithium battery.