11
\$\begingroup\$

Do batteries last longer with constant current draw or spiky current draw?

Or, as is implied by the accepted answer to "Making a battery last a long time in a microcontroller circuit", do some battery chemistries last longer with a constant current draw, while other battery chemistries last longer with a spiky current draw? And if so, which battery chemistries are which?

In other words: Say I have a microcontroller programmed to wake up and do a few things once a minute, and then go back to sleep for the rest of the minute.

Which kind of batteries last longer with minimum capacitance across the capacitor (so the battery sees a big current spike once a minute)?

Which kind of batteries last longer with a big capacitor (or some kind of LC filter) hooked up to battery (so the MCU pulls a big spike of current from the capacitor once a minute, and then the battery very slowly trickle-charges the capacitor)?

\$\endgroup\$
2
  • \$\begingroup\$ You might want to go look through the archives of Consumer Reports (you'll need to be a member to see everything). They've done a lot of battery longevity testing over the years, and when the recent generation of batteries intended for non-smooth draw applications came along they had a bit of catching up to do in their testing. It might behoove you to read up on what they've done. \$\endgroup\$
    – Michael Kohne
    Jan 16, 2011 at 2:59
  • \$\begingroup\$ Buy a pack of batteries and test it. :) Build a circuit that draws a spiky current and then connect a resistor across another battery to use the same average power. \$\endgroup\$
    – endolith
    Jan 20, 2011 at 22:30

2 Answers 2

Reset to default
3
\$\begingroup\$

This is a very good question and I don't have a good (complete) answer. So I'll just give you a tidbit one of my old bosses used in a design. There is a certain type of battery with very high internal resistance that he used for a long-life application. Since it's high resistance, it has low leakage and its charge won't dissipate well on its own, but you can't source a lot of current from it. Since it was a periodic application (similar to yours) he paired it with a supercapacitor. The cap would charge up and when the uC was ready it would turn on, perform its actions.

But for the life of me I can't remember the words he used to describe it. I've tried searching for low leakage, high internal resistance and other terms I thought it was but I can't seem to find exactly it. It wasn't a coin cell, but more like a AA (but it certainly wasn't that form factor). I perused the Wikipedia article in Lithium batteries and the closest I could find was the Lithium-Iodide battery. There's plenty of info in that article as well:

http://en.wikipedia.org/wiki/Lithium_battery

Many different chemistries and a comparison table. Good read.

Good luck!

\$\endgroup\$
0
\$\begingroup\$

For alkaline, it matters how much the peak is. Past a certain point the resistance goes up and you loose power there.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Any idea what this peak is for some standard cells? The closest indictor I've seen for this is Energizer's " Battery Selection Indicator " in all their datasheets, and they are qualitative. \$\endgroup\$
    – tyblu
    Jan 16, 2011 at 6:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.