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I designed a wearable with a 3.7V Li-Po battery (381018). Everything worked good at the begining and now after 6 months I realize some circuits are not charging anymore. For what I understood when I was doing a small research about this problem, I found out the overdischarge protection of the battery is 2.V6 and the battery management controller (MCP73831) has a UVLO of 3.45V.

1.-Is this the reason why they don't charge anymore?

2.-I talked with the manufacturer and they told me the highest overdischarge protection for that size of battery is 3.0V. However, i can't find a controller with lower UVLO. Any suggestions?

Note: I can't increase the size of the battery because the moulds are already made.

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  1. Hard to say.
  2. UVLO is not the same thing as overdischarge protection. From the datasheet of the controller you provided, UVLO monitor the difference between the supply voltage and battery voltage. "The UVLO circuit places the device in Shutdown mode if the input supply falls to within +50 mV of the battery voltage. Again, 150 mV above the battery voltage the MCP73831/2 become operational".

The UVLO kicks in when external supply falls to near or below battery voltage. The controller you mention is a charge controller, and has no function during battery discharge. If your cell voltage drops to 2.6, you plug it in to charge, MCP73831/2 checks the supplied voltage and it's 3.5v or more, it starts charging the battery. If the supply to MCP73831/2 is not good enough to keep up with the current demand when charging and the supply voltage drops, the controller stops charging. Check you charger supply voltage and power ratings.

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  • \$\begingroup\$ I read the battery of the ones that were not charging anymore. It was around 2.45V. but at the protection circuit output is 0V. The circuit has 2 pads that are not the ones used for charging. One of them is GND, the other one Vbat. Connecting them to 3V for some seconds recharge the battery to 2.7V and they can be charged again. (I know doing this is bad for the battery but it was the only way I could try to skip the charge controller). \$\endgroup\$
    – Gercer
    Mar 4 '20 at 20:45
  • \$\begingroup\$ As you mentioned in your original post, the over-discharge protection kicks in below 2.7V, so your cells are dropping past that and the protection circuit is doing its job properly. Depending on how much lower than 2.7V the cells drop and how often, what you choose to do to try and re-condition them is up to you - applying direct 3V is risky, but in non-critical application can be an acceptable way to get the cell up to the "acceptable" 2.7V for the protection to start allowing charge to flow into the cells. \$\endgroup\$
    – DSI
    Mar 4 '20 at 21:47

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