Battery Damaged

alessandromontanari

Hello,

I have uploaded my custom firmware to a Metawear R and then I left it without recharging for a couple of months.

Now it seems that the battery is not recharging.

Is it possible that the battery is damaged?

Thanks,

Alessandro

alessandromontanari

It seems that after deleting the firmware from the board the battery is re-charging again.

Any explanation for this behaviour?

Alessandro

Matt

@alessandromontanari

 The charger circuitry is completely independent of firmware control, and will charge regardless of the state of the microcontroller.

Something in your system is likely interfering with the trickle charge of the battery.  When LiPo batteries are severely discharged, it is advised to "trickle charge" them at around 1/10 the normal charge rate until they are brought up to their normal, safe minimum voltage.  Multiple over discharges is likely to damage the cell, so this prevents overheating and/or thermal runaway if there was damage.  All of our batteries come with a built in protection circuit to reduce and prevent over-discharge, but the battery charger still sees the cell as needing a trickle charge once fully discharged.

Getting back to firmware, the microcontroller will switch on before the battery charger fully exits trickle charging.  Depending on what the firmware does at power up, it may draw current exceeding the trickle charge current, which will be around 9mA as shipped.  That could cause the voltage to drop, the microcontroller to reset, putting the device in a reset loop as the process repeats.

Our firmware and bootloader have been thoroughly tested so that this is not an issue.  Generally, you should not have a problem unless you switch on high current peripherals (LED, Haptic) or high frequency advertisement shortly after boot. You can even run an infinite loop with the radio off and your current consumption will still be safe.

You could try removing things from your init process until the device boots properly, that is if a high current peripheral does not already come to mind.  If you need to recreate the trickle scenario, you could use a lab power supply with a constant current output set around 5-10mA.  Alternatively, remove the battery from a MetaWearR and the charger will trickle charge the capacitance on the voltage supplies each time it is plugged into a USB port.