Why are these batteries rated at 1.2v instead of 1.5v like all disposable batteries are.Also the chargers will only charge them to about 1.4v

Chemistry. Alkaline and lithium disposable batteries are 1.5V because that is the electric pressure of the reaction. NiMH rechargeables are always 1.2V and NiZn rechargeables are always 1.6V for the same reason. What matters more is the physics! Battery capacity SHOULD be listed in joules or watt-hours, but they show it in mAh because that makes rechargeables look better. 1.2V * 2,300 mAh = 2,760 mWh — and 1.5V * 1,840 mAh = 2,760 mWh. Those are the same capacity. A 2,300 mAh rechargeable has the same capacity as an 1,840 mAh disposable battery. Both batteries would theoretically power a 100W light bulb for 1 min. 39.36 sec — because 2.760 Wh / 100W = 0.0276 hours = 1 min. 39.36 sec. They use 2,300 mAh for marketing because that makes the rechargeables look 25% better than they actually are.

is the more Amh on a battery will be beter

Higher mAh is beneficial with devices that are high-drain. For example, a digital camera which will exhaust alkaline batteries in a period of hours or days, or a high-output flashlight. However, the highest mAh batteries have a higher rate of self-discharge and therefore do NOT give better performance in low-drain devices. For example, eneloop's Pro 2550 mAh performance battery has a self-discharge rate that is about 5 TIMES that of the regular 2000 mAh eneloop 2100. For regular devices, the standard battery gives better performance. For high drain devices, the high performance battery gives better performance. As neither do well with the reverse role, having the battery paired to the specific application is generally the best way to go.

Do these come charged or do you have to charge them before use?

It is a good idea to charge them before use but yes, they do come charged. All eight of mine were charged at 1.29 volts. As a matter of fact, I don't think I have ever bought a rechargeable battery that has not been charged. Even the cheap batteries from China come charged.

Can these be left on the charger 24/7 or should I remove them after a full charge?

I went on vacation for six weeks and forgot to take my energizer AA rechargeable batteries off the charger before I left. When I returned, there were no fires. Batteries were cool to the touch. And yes, they still work. Was their lifespan shortened? Not noticeably (I mainly use them for headphones, their charge measured 1.4v when I first removed them from the charger and 1.3v the following day) I usually get about five or six weeks of use out of a single battery in my headphones. I'm on week four right now and I don't notice any sign of low power. I'm too lazy to actually test the voltage and see if it's below 1.3v, but the headphones are sounding great which is test enough for me. I'm using a $10 Duracell charger I bought around 2012, so nothing fancy. Should you make a habit of leaving them on the charger? Absolutely not. Is it okay if you do? Well, these four year old batteries survived six weeks of constant charging without any 'serious' damage.

ASIN	B004QMXX4S
Batteries	8 AA batteries required.
Best Sellers Rank	#16,177 in Health & Household ( See Top 100 in Health & Household ) #57 in AA Batteries #1,546 in Sales & Deals
Customer Reviews	4.6 4.6 out of 5 stars (72,253)
Date First Available	October 27, 2005
Is Discontinued By Manufacturer	No
Item Weight	1.06 ounces
Item model number	NH15BP-8
Manufacturer	Energizer
Product Dimensions	1.16 x 3.69 x 4.51 inches

Rechargeable AA Batteries, Recharge Power Plus Double A Battery Pre-Charged, 8 Count

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