Thread by @max_guise

We've made a decision! We'll power the wallet with a lithium polymer (LiPo) battery, recharged via USB-C. We’ll provide flexibility: when the battery's depleted, the wallet will still work plugged in. Why'd we land here? Read on.. 🧵 block.xyz/wallet/battery…

https://twitter.com/max_guise/status/1486042221128257542

1/ When evaluating battery options, we anchored our decision on customer experience. In practice, a rechargeable battery option minimizes customer hassle and allows us to design the device to look and feel like the future of money.

2/ Why a battery at all? We're including features that will ensure the hardware is easy to use for everyone, even when the wallet isn’t in the phone's NFC range and can’t draw power from it. More on what this means in our next newsletter. Now back to which battery…

3/ We know that any device has failure modes, and we’re building an inclusive product that lives in context of other devices people use in their lives, not designing the wallet to be operated inside of a volcano. We need to expect that some devices will fail.

4/ So we’ll provide a recovery solution that keeps customer funds safe even when the wallet hardware is broken or lost. We’ll detail how that works in this self-custody system in a future post. With this approach to recovery in mind...

5/ Estimating and comparing the frequency of hardware failures we might expect for each battery option was less important to us in this decision than evaluating the customer experience during the wallet’s lifespan.

6/ Even with a recovery solution, field failures like a broken USB-C connector or a worn out LiPo battery are a hassle for customers to deal with. This is true for any battery choice, so we'll design the hardware to ensure a seamless experience for most people most of the time.

7/ We think many customers will pull their wallet out of a drawer after months or years of non-use, because the 2-of-3 multisignature design we are using will allow customers to safely use only their phone for more frequent transfers.

8/ In this setting a rechargeable wallet will work easily, or plugged in if the battery is depleted or degraded. We think this is a better experience than removing corroded AAA’s, scraping the battery terminals, buying batteries, and hoping corrosion didn’t damage the wallet.

9/ With a rechargeable battery, customers will depend on a power source and a USB-C cable when the battery is depleted. We think that’s OK - customers will only need to charge occasionally, as a result of the battery capacity and the multisignature design referenced above.

10/ Additionally, many customers will already have a charging plug and cable from other devices or accessories that require much more frequent charging, like the mobile phone the wallet is intended to pair with.

11/ No decision is perfect. Including a LiPo battery and USB-C connector comes with several limitations. We saw mitigating factors that meant these did not overshadow the customer experience benefits of rechargeable. More detail on this in doc linked at top of thread.

12/ In addition to AAA, we also looked closely at coin cells. We like that they’re compact and would allow us to seal the wallet well. But we found we’d need to take significant technical risks in order to compensate for their electrical limits, and we don’t like the experience..

13/ Finding the right coin cell replacement can be tough - there are model numbers to interpret and get wrong, the store might not have the right kind in stock, installing them can be tricky, and choosing the wrong one could result in degraded performance or damage the system.

14/ So rechargeable is right for our customers - time to build! We’ll ensure everyone is set up for success when using our product for the first time and over time. We have more consideration to do here for the global markets we'll serve and localis(z)ation needs for charging.

15/ We appreciate all of the input we received when we first shared information about the decision we needed to make - thank you to everyone who contributed. Scrutiny helps us build a better product. What decisions do you want to see next?