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I have a programmable TV remote control ( a Marantz I've had since 1999 or longer if it matters), it uses 4 AA batteries. I often find (at least when I use Li-Ion, non-rechargeables) that when the batteries die, only one is bad, the other three are strong. They are installed in series. I measure the voltage on each when I install them, there is not a big difference in open circuit voltage (lowest of about 1.65 volts, highest is 1.73 volts). When the batteries die, it is about 1.66 volts for three, and some hundreds of millivolts for the one that is dead. This has happened often enough to make me wonder.

Is the power demand concentrated on one when it starts to fail? Why does just the one get drained?

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at least when I use Li-Ion, non-rechargeables

Do you mean when using when using conventional alkaline batteries? Li-ion cells have a terminal voltage ranging from 3.2 to 3.7V, depending in the specific chemistry, and I'd be really surprised if you had a programmable remote from 1999 that uses Li-ion cells.

There are one or more things at play here--

1) In a series string of cells, there will nearly always be one cell that is depleted first. The usable capacity of each cell varies a bit due to manufacturing tolerances and a number of other factors, so there is always going to be one of the four that has the lowest inherent capacity and is the first to run out.

2) Some devices require multiple voltages internally, and rather than adding the cost of a converter, they simply tap the cells at a convenient point. For example, imagine a device that needs 1.5V and 6.0V. All four cells are drained in series for the 6V load, and one of the cells is drained an additional amount to supply the 1.5V load, sharing a common ground potential. For a programmable remote, this may be the case if the remote uses 1.5V to retain its memory or show status on an LCD, while using 6V for its transmit functionality. If the cell that dies first is always installed in the same position in your battery tray, I'd say that this is a likely scenario.

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  • \$\begingroup\$ I will pay attention to which battery is drained from now on. The Li-ion to which I refer is AA "Energizer Ultimate Lithium" and I assumed that meant Li-Ion, but it says"PILE LITHIUM" which I do not recognize \$\endgroup\$ – adam W Dec 30 '12 at 4:40
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    \$\begingroup\$ Ah, you're using lithium iron disulfide batteries. They're complete overkill in something like a remote control. Take a look at the advantages at the bottom of the first page here: data.energizer.com/PDFs/lithiuml91l92_appman.pdf They're best suited to high rate discharge and extreme temperature applications. \$\endgroup\$ – HikeOnPast Dec 30 '12 at 4:50
  • \$\begingroup\$ "Overkill" meaning the cost is not worth the longer lifetime? Also, there is some advantage to the lower weight, my remote holds 4 batteries towards the front, and it is a noticeable weight difference. Though I would probably care more about cost. Lifetime seems to be comparably longer, proportional to the extra cost. I used rechargeable AA's in the past (NiMh), I just got tired of the shorter and shorter usage time as they got older (and the heavier weight). As a side note, I love the speed the Lithiums give on RC cars, so I agree about the high discharge rate. \$\endgroup\$ – adam W Dec 30 '12 at 5:16
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    \$\begingroup\$ Lithium AA(a)s are suited for high drain applications, like digital cameras with flash or mp3 players. They are overkill, as in not cost effective, for low drain applications, like remotes or clocks or laser pointers. \$\endgroup\$ – Passerby Dec 30 '12 at 6:55
  • \$\begingroup\$ If one of the batteries consistently wears out first and weight is an issue, I wonder if it might be possible to use three lightweight "sleeves" to adapt three AAA batteries to AA-sized spaces (use a "real" AA battery in the spot that would otherwise wear out first). Using four matched AA rechargeable batteries would likely cause excessive wear on the one that's drained more, but using three AAA and one AA (and a charger that handles cells individually) might work well. \$\endgroup\$ – supercat Feb 4 '15 at 18:25
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A small difference in capacity of batteries means that one will "empty" first. That difference is not always obvious from a V check when new.

The difference between an AA alkaline battery which is 95% empty (say 1.4 Volts) and one which is very nearly totally empty ( eg, 0.6 Volts ) is the big difference which you observe.

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  • \$\begingroup\$ ah ok, that makes sense. I use rechargeables now so maybe I can mark which one seems to drain first. \$\endgroup\$ – adam W Mar 26 '17 at 3:49

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