I can agree that the low battery indicator is hypersensitive. .
I sometimes go anywhere from 2 to 3 weeks before replacing them.
I usually get two more warning windows before they go dead.
I tried rechargeable batteries – they lost their charge really fast and I felt I was replacing the rechargeable all the time.

I recycle other people's Alkaline batteries in my Mighty Mouse. The battery warning will pop a window up, but I usually get a couple weeks out of the batteries. Otherwise I use NiMH batteries. They give a battery warning with a week of charge remaining. Remember that NiMH (other than the new pre-charged type) loose their charge in one month even without being used...

I too used to use Rechargeable, but found out they the died too quickly. I started using the Energizer Lithium Ion batteries and they last for about 6 months before changing. I am going to give rechargeables another try though (try to be good about recycling). I found the Rayovac Hybrid rechargeables that peaked my interest, so I order a pair of 'em.

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Cheers:
Bob

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I highly recommend voltage testing disposable batteries before getting rid of them. An inexpensive digital multimeter works well for that purpose.

When my Bluetooth keyboard runs low on power usually at least one of the four original batteries still has nearly a full charge. I'll check if NiMH rechargables will work okay in that keyboard as soon as the current batch of alkalines I've reused runs out. I was getting about a month from 'em in a non-Mighty Bluetooth mouse before switching to a wired Mighty mouse (whose scroll pea hasn't worked for over a year, sigh, and stopped responding to any external methods of cleaning that had previously temporarily helped).

Rechargeables don't hold a charge long. They drain as they sit unused, so even when they're in the mouse and it's not being used, they're losing charge.

Try the Eneloop batteries. They're a new breed of rechargeables that don't lose their charge. I've been using these in my BT mouse & keyboard and they last much much longer... similar to alkalines.

I'll second the recommendation for Sanyo Eneloop batteries. They don't have as much charge in them to start off with (only 2000mAh) compared to some of the better NiMh which are 2500+ BUT as mentioned, they don't sit there discharging when doing nothing. They won't last as long in constant use theoretically but for keyboards, mice and cameras I find that in *practice* they last much longer.

Buy two sets and charge the second set. It'll still be charged months later when the first set runs out so you're not let down by a discharged second set of NiMh.

More than you probably ever wanted to know about batteries…

Part of the reason why people see that Apple's battery charge indicator is … well, let's just say MORE than conservative … is that Zinc-Carbon, Alkaline, and NiMH batteries all function differently. Let's first dispense with carbon-zinc because even if you could find them anymore, they totally suck for Bluetooth devices which are meant to be low-power. They're older tech than the typical alkaline batteries sold by Energizer/EverReady (same company!) or Duracell. If you stumble across them, they'll say "Heavy Duty" instead of "Alkaline" and the only reason they still make them is because alkaline cells die faster in high-current applications. You might find them in like D cells, but but probably not AA/AAA.

Alkaline are "nominally" 1.5 volts. Actually, fresh out of the package and not connected to anything, they may read as high as 1.65v, but they'll drop just as soon as you start using them. And they'll keep dropping, linearly over time at a constant power usage level, until they reach 0.9v (which is where they're basically dead. Dead alkaline batteries still having power drawn from them tend to eventually leak, and most devices won't work on less than 0.9 volts anyway, so … replace 'em at this point OK?)

NiMH batteries have a lower nominal voltage of 1.2v, as others have noted. This is why a freshly charged set of rechargeable batteries will tend to report back like 85% capacity in your Bluetooth menu. Yeah, they start higher than that and taper off, but they tend to spend most of their usable life between between 1.2 and 1.0 volts. Their discharge voltage isn't linear given a constant power draw like alkaline cells, and so the voltage warning thresholds for "buy new batteries if you need to", "replace them soon", and "could die any time now" are lower than alkaline, even if the "it's dead, Jim" voltage of 0.9v is the same either way. NiCd batteries work the same way, though … why are you still using NiCd? They're like carbon-zinc batteries—yes, there are still reasons to use them, but you don't need or want them.

The problem with NiMH/NiCd is that they drain (self-discharge) whether you use them or not. Within a month, they're flat. Enter the Low-Self-Discharge (LSD) NiMH cell! These are your Sanyo Eneloops, your Apple NiMH batteries (which are probably Sanyo), and some others made by TEnergy and a few other companies you maybe haven't heard of. They will last a YEAR or more in storage. Gen 2 Eneloops last longer than that. But they will eventually die, and if allowed to stay dead they tend not to come back to life when you put them in a charger. LSD NiMH cells are good. I wouldn't use anything else anymore.

Note NiMH cells are sometimes physically bigger around than alkaline cells. They're within tolerances, but sometimes the things you put batteries into … aren't. I'm thinking of a couple of headlamps I've owned for example… And for best results, don't use "quick" chargers on the batteries if you can help it. They tend to cut the lifespan of the batteries by as much as half! Apple's is basic but gets the job done. Sanyo's own work well enough. Maha and LaCrosse make the super awesome tweak knobs and charge odd numbers of batteries chargers. I'm gonna assume you're using the Sanyo or Apple chargers with your Apple or Sanyo batteries and call it good enough.

New kid on the block: Lithium AA/AAA made by Energizer. These aren't better for bluetooth devices than alkaline cells, and they're not rechargeable. These are gonna replace the carbon-zinc cells eventually and are meant for power-sucking applications. They're more expensive, though, for a disposable battery cell. The only reason I buy them is because if you can keep them dry, they have lower self-discharge than alkaline cells do, so they're good to have in earthquake-preparedness kits and the like, which is TOTALLY off topic.

FWIW, if you came to this hint looking for a means to tell the bluetooth menu that you're using NiMH batteries and to stop harassing you about replacing batteries that are nowhere near dead yet, sorry I haven't found it yet. :(