Where did my amps go?

I have a jumpstart pack, with a 17 amp lead acid battery. It is rather new and the battery is always full. But a while ago I went camping and it failed to light a CFL globe that only draws 0.9A, plus 0.3A for the inverter, for 6 hours. Where did the other 10 amps go? Can it be the battery, or the fact that the battery is not a deep cycle battery? I've read before that lead acid batteries are not made for prolonged use with low powered devices. But how can only 7 amps form a 17 amp battery be usable?

The nominal 17 amp-hours is probably at the 20 hour discharge rate.
The capacity at the 6 hour rate will be lower, although I would not expect a more than 50% decrease. 7.2AH out of 17.

You will never see the full capacity of a Pb battery, just to add to what inetdog posted above, you should not discharge a Pb battery below 11 Volts.

It sounds like the battery dropped below the minimum operating Voltage of your inverter.

It is typically considered wise to use just 30% – 50% of the rated capacity of typical lead acid "Deep Cycle" batteries. This means that a 600 amp hour battery bank in practice only provides, at best, 300 amp hours of real capacity.
If you even occasionally drain the batteries more than this their life will be drastically cut short.

Norm

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Noted. I just think it would have been better if manufacturers could mention the actual usable AH on the batteries as well.
So when you buy a 102A deep cycle battery, you actually only have a 50AH battery? This is not good news:shakehead

lightseeker2009 said:

Noted. I just think it would have been better if manufacturers could mention the actual usable AH on the batteries as well.
So when you buy a 102A deep cycle battery, you actually only have a 50AH battery? This is not good news:shakehead

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It gets worse. When discharged as low as 50% SOC the total number of discharge/charge cycles the battery is good for will be drastically reduced.
For a battery which gets cycled daily (most off grid uses) you should not plan on discharging more than 20% on a daily basis.
Batteries other than lead acid may allow heavier usage and a longer delay before recharging.
PS: if your battery gets used only once a week, going down to 50% may not be too bad.

I've ready that for off-the-grid applications (i.e., daily use), you shouldn't go below 70% charge. 50% only if absolutely necessary. Below that, and you're damaging your batteries.

However, if it's an emergency, obviously you'd drain them as much as you need. So, a 102AH battery does have that much capacity, but you really shouldn't use more than 30-50AH if you don't want to damage it.

Every time lead acid batteries get discussed on CPF the arm chair expert all come out and regurgitate what they have read but for all that no one is really considering the post.

Unless:
- inverter is cutting out early
- too large of voltage drops in the wiring (my second guess)

Then you are right it should last much longer.

My first guess(es) is the unit spent too much time on the shelf and the battery is partially sulfated, exasperated by the built in charger that is probably not getting the voltage up high enough to prevent sulfation ... Or boiling the battery ... Take your pick.

SemiMan said:

Every time lead acid batteries get discussed on CPF the arm chair expert all come out and regurgitate what they have read but for all that no one is really considering the post.

Unless:
- inverter is cutting out early
- too large of voltage drops in the wiring (my second guess)

Then you are right it should last much longer.

My first guess(es) is the unit spent too much time on the shelf and the battery is partially sulfated, exasperated by the built in charger that is probably not getting the voltage up high enough to prevent sulfation ... Or boiling the battery ... Take your pick.

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Yes, it can be any reason like you mentioned. The inverter does have thin wires. Very thin. But the load is so low, I never came close to 20% of what the inverter can manage.
Maybe it can cut out too soon.
Lastly, I don't charge it with the supplied adapter. I always fear an overcharge as I don't know if it can terminate charge successfully after a full charge. I once charged it for over 48 hours but it never shut off. The manual suggested charging could take ''a couple of days''
Therefore I use a hobby charger to charge it. I set it at 1.0 amps which is double the rate of the supplied adapter, but I figure 1.0A is still low enough for this battery.

A hobby charger with a proper lead acid multi-stage charge cycle ?

Best you can do is measure the voltage drop on the cables and see what you are losing.

If it takes "days" to charge then I would be more worried about under-charge in most cases. It is probably a fixed voltage float charge. Its better to charge with a multi stage charger that gets up to higher voltages.