[gmcjetpilot]

I have a box of old 9v bats from smoke alarms and such. Well many are in the 8's, 7's volts but most around mid 6 volts. They should be good for something?

Well The Davtron M811 clock has a memory stay alive input of 6 volts. They use to sell an expensive 6 volt mercury battery, which which is just attached (soldered) to wire leads outside the clock. Davtron now recommends (4) AA's and make it yourself. Most new Alkaline 1.5 volt bats start out at about 1.6 volts, so (4) will give 6.4 volts, which is safe. I called and asked for max volts. They said 6.4 volts would be fine, but couldn't give me a max voltage. However connecting standby leads to ship power (12.5-14.5 volts) leads will cause damage apparently.

What other uses for an old 9v volt battery, run down to about 6.5 volts, are there?

Before you say it will not work it does. I just got done with testing a 9 volt battery (starting at 6.45v). It lasted 6.5 months in my Davtron M811 clock. It was still going, maintaining time. The final volts was about 3.8 volts.

There might be some other uses for old batteries?

Even though 6.5 months is about half or a third of a new pack of AA's, its not bad. The nice part of using the 9v (6.5 volt) is its free, small and connects with small battery clip.

Any old battery use suggestions?

 

[Ironflight]

You could probably use them to power LED map lights and the like (stuff designed to run on USB power).

Put a couple in series and use them to drive a D10A for some short period of time?

 

[CESSNADON]

The best thing you could do with the batteries in question would be to put them in the recycle bin. Reading the voltage of a battery with a dvm without the battery being loaded will give errorenous info. I'll be williing to bet that if you took the battery that is indicating 6 volts and put a load on it the voltage would drop, probably close to zero. The battery has served its purpose let it RIP.