How many still use a hydrometer to measure the specific gravity in their battery? How do you know your battery is still holding a charge?
I have a battery hydrometer and a radiator coolant hydrometer. I have not used the battery one in several years since all the batteries that I buy now are sealed.
I just looked on Amazon, you can get one for under $20. Back when I was young and poor I would keep battery acid and fool with such things, but in the end it only delayed buying a battery.
Ron the Coilman
I use both.
Volt meter alone gets me into trouble all the time. I've set up a 55W fog lamp to check the battery under a load. Many batteries will indicate 95-100% charge but won't light a bulb much less crank an engine. They can show full voltage but won't provide any current. With about 10 vehicles and tractors to maintain, I'm slowly adding trickle chargers to all of the tractors and the vehicles that don't get used often.
On a side note, anyone else notice that new batteries are now carrying no more than a 12-month warrantee? Many have only a 3-month warrantee! (I'm looking for two tractor batteries now.)
Specific Gravity may also get one in trouble. If for instance some of the water has gone out, the SG would be higher. With airplane batteries, I use both SG and a volt meter. I check them after they have been serviced to the proper level and charged allowing time for it (next day) to set and rest. I also, like Ken place a load across them for a few minutes before reading voltage.
1.265 is normal for a fully charged one (at 78 degrees) but often, deep cycle batteries are higher slightly. The problem with a SG that is too high is corrosion that will kill the battery sooner than it should.
There is a big difference in the state of charge from 6.3 volts to 6.2. About 25%. A battery reading of 6.0 is 75% dead.
As I recall from my auto shop teaching days, the specific gravity is 1280.
1.280 would be deep cycle. Some of those can go 1.3. The garden variety (non deep cycle) car battery is 1.265 fully charged.
Aircraft batteries do not necessarily have the same specific gravity as automobile batteries.
I didn't imply that they did. I merely stated when I am servicing an A/C battery I use both the hydrometer and voltmeter.
The standard non deep cycle lead acid such as a group I six volt is 1.265 at full charge at 78 degrees.
Aircraft batteries are typically deep cycle and fully charged are in the neighborhood of 1.275 to 1.295.
A quick check when someone says their car won't start. Turn on the head lights, see that they are well lit, and hit the starter. If head lights go out or dim significantly, you likely need a new battery.
I use a load test voltmeter and specific gravity checker.
A load test meter should hold the same voltage for at least 10 seconds or the battery will not doubt not do the job.
When the specific gravity is up to 1265 it's time to disconnect the charger.