Using 2-cell lead-acid battery as direct replacement for single-cell lithium-ion battery

Question

I've designed a system that remotely logs some data (position, some weather data, etc.) in remote areas that currently uses a single lithium-ion battery (~850mAh) that is recharged via a solar panel with a BQ24210 solar charging IC that stops charging when the battery reaches 4.2V. The system wakes periodically throughout the day to transmit data and consumes roughly 50uA while sleeping. The BMS I have on the board (TI BQ29707) has an overvoltage lockout at 4.28V and an undervoltage lockout at 2.8V. So far, the system works well and performs as expected.

However, I have realized that the weather at the testing locations is much more volatile than the lithium-ion battery is specified to operate in (can easily reach over 110°F and below -10°F each year). Because of this, I am looking for alternative batteries that won't require a board redesign.

I have found some 2-cell lead-acid batteries that have a much larger capacity than what I need, but have a more relaxed temperature range. According to this article, it appears that lead-acid cells have a range between 1.93V and 2.15V which results in a 2-cell lead-acid battery having a voltage range of 3.86V and 4.3V.

Will I run into any issues making the substitution to a 2-cell lead-acid battery in my system? Size and weight are not a big constraint in this scenario.

Answer 1

Your charger won't work at all well, as the limiting voltage is too low to properly charge a 4V lead acid battery. You'll need something like 4.6 to 4.8V.

If discharged down to 2.8V, the battery will be totally flat. Unless recharged soon after, it may never properly recover. Even if it is charged soon after, expect a life well below what's normal for a lead acid battery.

If you want the system to work, you will have to change the charge voltage and undervoltage lock out. And make sure the circuit being powered can handle the higher voltage while charging.