LiFePO4 battery fuel-gauge for a BLE design

Components & Accessories Power
1

Hi I’m considering using a (roughly 400mAh) AA-sized LiFePO4 lithium iron phosphate battery for a design. I will probably use a fuel gauge to monitor the battery for safety, but I have 2 questions about this design and wanted to get everyone’s input.

  1. if users ignore my instructions to use the provided LiFePO4 battery, and instead they use a plain old AA alkaline battery… what kind of problems can happen with the fuel gauge? I’m thinking of using one of Texas Instruments’ bq-based fuel-gauge solutions, so idk if/how it will even detect that the battery is not the correct chemistry. The other problem would be if they try to charge this AA alkaline battery - and this sounds like a fire hazard.

  2. there are 2 sides to this design - the remote controller, and the “hub”. The hub will have a BLE at 3.3V, but the remote controller is powered off a battery as I just described above. Can I just use the direct battery voltage on the BLE, and not go through a voltage regulator - so the BLE module will get about 3V to 4.2V input? (which is within the acceptable input voltage range of this BLE module - since it can take 1.7-5.5V input). So the question is: what happens when one BLE module runs off 3.3V, and the other paired BLE module runs off 3V to 4.2V? Will it even properly make a connection?

Thanks for your input and help.

2

1- Probably nothing, but a AA battery is going to show up to a fuel gauge as a really dead LiFePO4. Unless your charger is intelligent enough to detect something is wrong, trying to charge a AA battery with a LiFePO4 charger could cause a fire or the battery to explode.

2- As long as your BLE device can operate in the voltage range provided by a LiFePO4, it’s not going to care if you regulate it’s power source or not. BLE devices are not aware of and don’t care what voltage a paired device runs at so no problem there.

3

Thanks for your response, and input.

  1. I was thinking something similar if someone plugged in an Alkaline battery – and that makes sense.

  2. So both BLE modules should be able to link properly …even if each BLE module is operating at different voltage levels. Good to know. So I don’t have to worry about adding a voltage regulator or DCDC converter in between them. Or maybe I’ll put an optional 2.5V or 2.8V regulator in between (tbd)