Charging Li-ion batteries in parallel

Charging Li-ion batteries in parallel

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I wanted some opinion on my set up here, just to make sure I got the basics right.

I have a Li-ion battery charging circuit based on the MCP73113. This is designed to be a single-cell battery charger.

The battery itself (3.7V, 650mAh) comes with its own PCB with Schottky diode and current regulators as protection. EDIT: Not a Schottky diode. Current limiter and a Protection IC.

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The primary purpose of the setup is to ensure all individual cells work cohesively. However, I've acquired additional batteries from the same manufacturer and aimed to boost capacity by arranging two cells in parallel. Despite each cell having its own PCB, I retained just one PCB for the combined cells by soldering their leads together. This method seems to enable identical charging and discharging processes to standard single cells (3.7V, now 1300mAh).

Nonetheless, there's a notable failure rate—approximately 20% in every 10 packs created. Initially, these packs function well, but issues arise when they aren't charged for extended durations or after being fully discharged, leading them to malfunction. In one particular instance, a pack showed varied voltages, with both cells dropping below 2V, rendering them inoperative.

I realize my current approach may not be conducive to achieving a consistent 100% success rate. I seek guidance on how to resolve this issue. Available controllers seem optimized for series cell configurations, not parallel. Am I fundamentally overlooking a critical aspect?

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