Battery Charged?

[Van Go]

After 48 hours on the charger, and rested 8 hours, my voltage read 12.9 volts. What does this tell me about the condition of my battery?

 

[WheelEstate USA]

It tells you the volts stored at this time. You need a hydrometer (less than $5 for simple one) to know the actual condition.
If it bounces back after a load Chances are its ok.

 

[Van Go]

Ishould have mentioned that it is a sealed, Optima battery. Can't check electrolyte.

 

[WheelEstate USA]

What kinda battery ya got ??

 

[Van Go]

The battery is an Optima blue top

 

[WheelEstate USA]

If you do a forum search you'all find better answers on the CPAP.
You need to know what your machine draws.
Howdo you plan to keep the battery charged?

 

[WheelEstate USA]

Was typing while you posteb about battery.

 

[Van Go]

If you do a forum search you'all find better answers on the CPAP.
You need to know what your machine draws.
Howdo you plan to keep the battery charged?

I'm going to run a generator. Several hours a day. Will run a factory installed converter to charge the battery.

 

[Van Go]

[font=Verdana, Arial, sans-serif]I'm going to run a generator. Several hours a day. Will run a factory installed converter to charge the battery.[/font]

 

[WheelEstate USA]

Shouldn't have any problems with a genny but there is better advice from other CPAP users here on the forum.
Possibly someone will pop in.

 

[SternWake]

12.9v several hours after the charging source is removed indicates a battery at or very near fully charged. Fully charged battery voltage can range from 12.6 to 13.15 depending on the specific battery. AGMs usually are the ones which are over 13 volts.

However it tells nothing about the remaining capacity of the battery.

An older battery is like a gas tank which keeps getting smaller as it ages. You can still fill it up, but it does not hold as much gas as when it was new.

A capacity test is a rather involved procedure requiring tools and patience to arrive at a number to determine actual remaining capacity.

The load testers the autoparts stores use test only cold cranking amps, which is not indicative of remaining capacity, and less so on a deep cycle AGM battery.

When a battery loses voltage quickly after being charged it is a sign of weakness, but just because a battery holds higher voltage after charging does not mean the battery is at like new capacity.

Voltage is not a great indicator of battery health or remaining capacity or state of charge for that matter. However, many people believe so.

 

[Van Go]

Well, this particular battery sat for 1.5 years being charged once or twice. I guess the best way to test it is to put a load on it and see what happens?

 

[SternWake]

For a fairly accurate capacity test Divide the battery's rated amp hours by 20.

Apply that number of amps to the battery for 10 hours, and remove load, and wait for voltage to rebound. If it is in the 12.2v range ~2 hours later, the battery is likely still near its original rated capacity.

You can guestimate health by applying any somewhat significant load to it and just seeing how much the voltage drops in that load. If voltage tanks quickly to 12.2v or less, the battery is not very healthy, but it of course depends on the size of load the battery is trying to power.

A healthy and fully charged 100 AH battery can power a 5 amp load for 20 hours at 77f degrees before voltage drops to 10.5v, which is considered 100% discharged

 

[Van Go]

OK. As soon as the inverter gets here, I'll run it off the battery for overnight and see what the voltage does.

 

[Sabatical]

Optima claims their batteries aren't negatively affected by sitting unused...for what that's worth. I used two d31m optima's in a sharpening van setup. I was very pleased with their performance. I didn't do any math to know true performance. I just knew that I was able to work as long as I needed without the van running. The first set lasted three years with just alternator charging. I had noticed a loss of run time so I replaced them and also added a Pro Tournament smart charger which I then plugged in at night.
I guess at the end of the day if it fills your needs and it's what you have, then it's perfect.