--- a/FC-handset-spec	Fri Jun 11 01:47:22 2021 +0000
+++ b/FC-handset-spec	Fri Jun 11 04:34:26 2021 +0000
@@ -680,3 +680,30 @@
 Because our firmware will be designed for a simple on/off vibrator control,
 during fw development on the Venus board it will be trivial to use a LED to
 simulate the vibrator on/off state.
+
+1.10. Battery
+
+The battery in our FC Libre Dumbphone handset will be single-cell Li-ion.  It
+goes without saying that this battery will be freely removable and replaceable
+by end users.  The specific size, form factor and mAh capacity of this battery
+won't be addressed until later in the project, when we get closer to building
+the actual handset.
+
+Our Calypso+Iota chipset dates from the era when the cellular handset industry
+was transitioning from NiMH to Li-ion batteries, and the Battery Charger
+Interface (BCI) block in the Iota chip supports both battery types, or at least
+TI's documentation claims so.  Given that we are going against the mainstream
+society's ideas in so many other ways, I have given thought to the possibility
+of using a NiMH battery instead of Li-ion.  However, the problem with using a
+NiMH battery is that we would be going into completely uncharted territory
+without any guidance.  In the case of Li-ion batteries the charging process is
+well-understood in both theory and practice, and our FCHG logic based on reverse
+engineering of Pirelli's firmware works well both on the same Pirelli and on
+Motorola C1xx family.  In contrast, if we went with NiMH, we would have
+absolutely no guidance in implementing the necessary charging control logic
+(TI's LCC code is useless), causing a huge risk to the project.  Furthermore,
+determining the state of charge from Vbat for the purpose of the bars icon is
+already somewhat challenging even with Li-ion, given the relatively flat middle
+part of the discharge curve - and with NiMH we can only expect the problem to be
+even worse, as their discharge curve is said to be even flatter.  For these
+reasons, we are going to play it safe and stick with Li-ion.