Need Advice RE Diode for Battery

[Wireflight]

Greetings, All!

I have a cordless phone that uses a 2.4V NiMH battery pack that has died. On disassembly of the battery, I discovered the battery is basically two AAA cells that have been wired together, with a short 2-lead cord and a modular connector to connect the battery to the phone. Since I have several similar phones, I am toying with the idea of modifying the phone to accept a pair of ordinary, single-cell AAA NiMH batteries; however, that's going to require more fabrication than I presently care to do: I have ordered tabbed single-cell AAA NiMH batteries that I intend to use to build a replacement battery pack.

I'm not confident the circuitry in the phone will shut off the phone before either of the cells is completely drained, and I want to protect the battery from cell-polarity reversion. It seems reasonable that I could effectively guarantee to myself such protection by using a diode (electrically) between the cells. Alas, I don't know what diode is best for this, so I'm asking the members of this forum who are knowledgeable in this area to please so advise me. Also, if I'm headed in the wrong direction, in terms of technology, please let me know.

This began as a cost-saving project: I didn't want to pay $17.11 per battery at my local Wal-Mart for a single phone battery (I need at least 5); I figure I can build my own slightly-less-pretty but just-as-useful batteries for less than half that: considerable savings! Unfortunately, my initial search of Amazon revealed prices as bad as those of Wal-Mart; after I ordered the cells, I found on Amazon a 2.4V NiMH battery I can use, for about 90 percent of what I will have in the price of the parts to build my own -- and with it, I wouldn't have to build anything.

<sigh> Hindsight.

Anyway, I'm wondering whether using a diode between my cells will provide me with the sort of protection for which I'm looking, and (assuming the idea is not technically flawed) which diode to use for such purpose.

Thanks in advance for all your assistance!

Wireflight

 

[BobK]

Why would you want polarity protection if you are not replacing the batteries on a regular basis? Just make sure they are correct when you install them.

A diode would drop some voltage (about 0.6 for a silicon diode, 0.3 for a Schottky diode) so this is a significant drop from a 2.4V battery. If you really think you need one, the Schottky is preferred.

Bob

 

[Wireflight]

Hi, BobK.

Thanks for the prompt response!

In RE my train of thought -- and this may seem a bit retarded -- but how much power can a diode use? I mean, let's assume that watts is fixed; if E drops by 0.3V, then I must increase proportionally. So, basically, I'm looking at an initial power consumption, from the battery's perspective, of 8/7 times the base rate (i.e.: 2.4/2.1). Wow -- that has a built-in pun! Anyway:

Since the application is a phone that will almost always be on the charger, I only take the hit when the battery is in a net-discharge condition, yes? Or no? I don't know.

Meanwhile, the battery doesn't self-destruct if discharged below the point that it's polarity is preserved. I realize the diode will leak a little, but in the grand scheme, shouldn't that be negligible?

Thanks again, and I look forward to learning more when I return (I have to be away from the computer for a few hours).

Sincerely,
Wireflight

 

[BobK]

If the battery is in a device that keeps it charged, putting a diode in series will prevent it from charging!

Bob

 

[Wireflight]

If the battery is in a device that keeps it charged, putting a diode in series will prevent it from charging!

Bob

Okay, now I'm really going to seem stupid: aren't blocking diodes so used in PVA-charged batteries? Those people seem awfully concerned about polarity reversion. Granted, they're dealing with greater system voltages and currents than I, but if the principle is truly sound ....?

What am I not "getting"?

Update:
=========== RATS! I just tried drawing a schematic of what I had in mind. WTH was I thinking? ===========

Okay, so a simple single-diode addition to the circuit is a ridiculously bad idea. I have a feeling that, if I start looking for a polarity-preserving circuit on a chip, I'll be defeating my cost-saving and eco-friendly intent. Oh, well.