Perfect battery Setup

[Steven987]

Looking for a good batter setup wanted to use nimh batteries but i cant go as low as 2,7V cause of the 8MHz 328P and as high as 3,9 limiting from the RFM69.
so 3 nimh AA would be to high when fully loaded (1,5 x 3 = 4,5V) and 2 nimhs are to low for the arduino when disscharged (1 x 2 = 2V).
What is a good setup?

[mfalkvidd]

@steven987 to know what is "perfect" for your specific use case, we'll need to know more about the use case. How much current will the node need? How long battery life are you aiming for? Will the node have a solar panel or something else to charge it? How small do you want the node to be? How much money are you ok with spending? If you have a power source (solar panel, etc) what is the max voltage delivered from it? Does the node have any sensors? If so, what voltage requirements do these sensors have?

Nimh have a high self discharge (around 30% per month) which disqualifies them for low-power nodes that don't have a way to charge themselves.

Btw, the operating limit for 8MHz atmega328 is ~2.34V but you'll have to change the BOD settings to go that low.

For some of my nodes, the "perfect" setup is 2xAA alkaline and throw them away at 2.34V. Gives me a fairly small node and 5-10years battery life.

In some cases, using a dc-dc booster for the mcu and direct battery connection to the radio is a good solution.
In some cases, using 3 batteries in series for the mcu and sensors, while only using 2 of the batteries for the radio is a good solution.

[zboblamont]

@steven987 The @mfalkvidd response is spot on, without a means of charging, your solution has more problems than using straightforward alkalines.
There are a few articles around examining decay and capacity of the various battery types, well worth googling, together with a power-sipping sleep routine they can get some extraordinary life-spans.
The custom board I bought in got round the BOD problem by incorporating a booster and ldo, so it can be done if you have the expertise, but I don't.

[Steven987]

@mfalkvidd Im aiming for the LSD (Low Self Discharge) Nimhs like eneloop pro wich have still 85% after 1 year so 15% over a year.
Use case is a weather station readouts every 5-10 minutes. Current consumption i will measure later.
Sensors are SHT31, BMP280, Rain Gauge and Anemometer.

SHT31 2,15V - 5,5V
BMP280 1,71V - 3,6V
RFM69 2,4V - 3,6V

[mfalkvidd]

@steven987 ok. Then the self discharge will be the main battery consumption, so you don't need to worry much about the other parameters.

[ncollins]

@steven987 I would argue the perfect battery setup is a single AA or AAA LiFePO4.

• No boost or regulator needed, nominal voltage: 3.2v
• Much safer than traditional LiPo/Li-ion
• Really easy to solar charge with TP5000 module and cheap solar cells

Cons

• they're not super available
• a little pricier
• require a LiFePO4 charger
• still potential for fire with enough abuse
• Significantly less power density than NiMH or alkaline

LiFeP04 Batteries
https://www.ebay.com/itm/12X-SOSHINE-LIFEPO4-AAA-10440-BATTERY-280MAH-3-2V-FOR-WIRELESS-MOUSE-ALARM-TOY/333294469931?hash=item4d99e6032b:g:lk0AAOSw04ddULoH

TP5000 Charging Module (I use for solar charger)
https://www.aliexpress.com/item/32807030878.html

Solar Cells
https://www.aliexpress.com/item/32882323830.html?spm=2114.12010612.8148356.16.192a59c23u0hej