EYE ON NPI - Panasonic's VL/ML Series Lithium Rechargeable Coin Batteries

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9d ago 10:35

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This week's EYE ON NPI is looking at itsy-bitsy-teensy-weensy little rechargeable batteries that can keep your micro-power electronics running for many years without needing any maintenance from your users: it's Panasonic's VL/ML Series Lithium Rechargeable Coin Batteries (https://www.digikey.com/en/product-highlight/p/panasonic/lithium-rechargeable-coin-batteries). These are small, solderable batteries much like the coin cell batteries you're used to replacing in watches, toys, and other gadgets..but this time they can be recharged in-circuit to make maintenance effortless. We've covered lots of batteries and battery holders on EYE ON NPI - from enormous lead acid batteries to tiny coin cells (https://www.digikey.com/en/products/filter/batteries-non-rechargeable-primary/). These are an essential part of the engineer's repertoire as so many products need to work when not plugged into the wall. We use coin cells a lot in our design work: there's nothing as compact and they have great energy density. But they're typically 'primary cells' - not rechargeable. That might be fine if you're using them for something like a remote control (https://support.apple.com/en-us/101261) or a small toy. But they do eventually need to be replaced, which can be a user frustration. For that reason, many products that used to have primary cells like AA's or coin batteries have slowly transitioned to embedding lithium polymer pouches. You can get rechargeable lipoly batteries in 100 mAh or less! (https://www.digikey.com/short/7njnd057) However, there may be some cases where you still want something really really tiny, like say 9mm diameter and under 1mm thick - a size only achievable with a coin cell - but without dealing with removing and replacing a battery every few weeks or months. Especially if we're talking about something that is going to be plugged in once in a while, or where the coin cell is a fall-back. This comes up often with devices that have real time clocks (RTCs) - such as clocks, computers, laptops, tablets, watches, GPS units (https://www.adafruit.com/product/5440), etc. They might have a main battery or power system that can run a microcontroller/CPU and display plus peripherals, but you still want to keep time and maybe an alarm setting when the main power cuts off. Historically, folks have just used coin batteries - ideally replaceable ones - but sometimes not as in the case of the DS1287 (https://theretroweb.com/chip/documentation/ds1287-647b3602989d3299594321.pdf) which had the coin battery sealed inside! If you're designing a product today that needs an RTC battery, we'd say take a good look at the Panasonic's VL/ML Series Lithium Rechargeable Coin Batteries (https://www.digikey.com/en/product-highlight/p/panasonic/lithium-rechargeable-coin-batteries). No holder required: they come with tabs to solder directly onto a PCB in vertical or horizontal orientations. And they come in a variety of sizes from the 20mm / 45mAh to 12mm / 7mAh and even smaller. Note that as expected, you're going to get less capacity than a primary cell, so these are good when you think you'll get recharged every few days or weeks. Don't forget: you will absolutely need a proper lithium charger to recharge these batteries. We've got plenty of charger breakouts you can use, we particularly like the bq25185 (https://www.digikey.com/en/products/detail/adafruit-industries-llc/6091/25805553) which you can easily configure for the 1C current charge rate to match your Panasonic Lithium Rechargeable Coin Batteries (https://www.digikey.com/en/product-highlight/p/panasonic/lithium-rechargeable-coin-batteries) They can all handle 1000+ cycles, we like the bq in particular because it has power-path which will help avoid unnecessary discharging/cycling. Ready for a tiny burst of power to keep your clocks a-tickin'? You can pick up a wide selection of Panasonic's VL/ML Series Lithium Rechargeable Coin Batteries (https://www.digikey.com/en/product-highlight/p/panasonic/lithium-rechargeable-coin-batteries) at DigiKey right now! They're in stock in a range of sizes and configurations for immediate shipment - don't forget that like all Lithium batteries you may need to ship ground, so order now and you'll get those bite-sized batteries shipped within the hour for immediate integration. See it on DigiKey https://www.digikey.com/short/wb83dfff

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