Battery status

Hi!
I just made an interesting thing: used a roller battery and hooked it up with cheap desktop speakers. So now I have a portable speaker, if I calculated right then I have a portable 10W audio system
But I'm worried about the battery, the battery was dead before I added electrolyte to cells, now I get 12.8V and 8.3A with my multimeter.
So how could I know when the battery is, for example, half-charged etc? I thought to buy a cheap ammeter and hook it to the battery, but I can't leave it there the whole time, because even with my multimeter the wires got hot.
Is there a small device or circuit board that would indicate how much the battery is charged? (not needed to be digital, could be just few LEDs).

An ammeter has a low resistance; if you connect an ammeter across the battery you are effectively shorting it out - it generally won't like it & you are draining its charge. An ammeter is normally connected in series with the load - but this is not useful for measuring battery charge remaining.

I've got no idea what a 'roller battery' is, but most battery types have a terminal voltage that relates to the charge remaining.

Eh, maybe called differently in english... scooter, moped, bike battery, it is like a car battery, only smaller.
So I should get a voltmeter? The only place I know where to get cheap parts is ebay and there I can only buy a multimeter for 3$

A multimeter has the voltmeter function built in, so yes it will do the trick.

Well, according to Battery Tutorial, the following charge percent & voltages apply for lead acid batteries:

100% 12.7
*75% 12.4
50% 12.2
25% 12.0
Discharged 11.9

Thanks!
Will write down those numbers on the box, but will try to find simply a voltmeter, it will be a shame if I won't use a good multimeter right

With only 12.8V, a single-ended stereo amplifier produces only 1.2W per channel at clipping into 8 ohms or a maximum of 2.4W with a horrible-sounding full blast square-wave.
It might produce 2.0W per channel into a 4 ohm speaker at clipping.

If the amplifier is bridged then it might produce 4.2W per channel into 8 ohms at clipping.

Who lied about 10 Whats?

audioguru said:

Who lied about 10 Whats?

Click to expand...

Maybe a very conservative PMPO figure.

PMPO is phoney baloney power.
Peak is simply one number doubled.
Music Power is rated at a very high distortion level only for a moment before the power supply sags or before the amplifier blows up.

Real power is RMS continuous power into a certain load resistance at a certain very low distortion from 20Hz to 20kHz with all channels operating.