Rechargeable coin batteries for nRF52 DK?

[Ladasky]

Hello,

I have a need to construct multiple portable devices on a short time frame. We expect that building Arduino-format shields for our peripherals and using nRF52 DK boards will be the quickest way to accomplish our task.

These devices will see heavy use, so we don't want to use disposable batteries. Previously, I asked about using lithium polymer batteries to power the nRF52. I was informed that the upper safe limit for the chip is 3.6V, so a LiPo battery (which, when fully charged, can reach 4.2V) would certainly damage it.

Here are my current questions:

1. what RECHARGEABLE COIN batteries are safe to use on the nRF52 DK boards?

2. Is anyone actually using rechargeables, for example, lithium-manganese ML2032 batteries? I am looking at the ML2032 because its nominal voltage is slightly lower than the more common LR2032, and some spec sheets show the LR chemistry going over 4.0V at high states of charge and light loads.

3. If you are using rechargeables: how do you recharge your batteries? I have encountered many vague web pages which hint that all coin battery rechargers are not the same. They must be matched to battery chemistry. I am not entirely certain of that, however, since when I try to shop for coin battery rechargers, their specifications are not clear.

I am looking at the PCA10040 schematic, and the only thing I see in the battery circuit is a safety diode. But that may help. The diode contributes about a 0.5-volt drop, according to my measurements with a disposable CR2032 battery. So if I read 3.1 volts across the battery, when I use it to power the eval board I get around 2.6 V across VDD and ground (running Blinky, it is surprising to me how much that voltage fluctuates as the LED's switch on and off, but that's probably an issue for another day.) This suggests that coin batteries up to 4.1 V can be used on the eval board. That could possibly allow any lithium battery chemistry, except for LiPo. Can anyone confirm that?

Thanks for any advice and suggestions.

[Ladasky]

We are developing prototype wearable devices. The nRF52 will be our SoC. However, we can't solder QFN or WLSCP packages in-house, and we aren't ready to commit the funds to stuffing custom 4-layer boards just yet. Sure, there are other Arduino boards out there, but they don't have an nRF52 chip on them. And right now, we want to test our peripherals.

The unreleased Arduino Primo Core appears to be intended to accomplish pretty much exactly what we are trying to do. Nordic has delayed that product. I wonder whether they have delayed it so that they can put the nRF52840 on it instead of the nRF52832. Among other advantages, the nRF52840 appears to accept an extra few tenths of a volt on VDD. That should make it safe to power the chip from the rechargeable lithium battery chemistries that I have concerns about.